Do I need a China visa when I fly from Japan to China as a U.S Citizen

No, it sounds like you’ll be in transit rather than a true visit. If you are staying for less than 24 hours then you can do what is called transit without a visa. More info here : https://www.travelchinaguide.com/embassy/visa/free-transit-24hour.htm

If you were staying more than 24 hours then you would have needed a visa as an a American citizen to visit China. You can’t easily get one in Japan so you would need to return to the USA in order to get it.

The two other answers give conflicting information. I looked at the website of the Chinese embassy in Japan (with some help from machine translation), and the information there agreed with neither of these answers, because it said that you would need to apply for an entry permit at the border in order to transit without a visa.

Therefore, it seems like a good idea to consult TIMATIC, the database that will be used by the ground staff when they decide whether to let you board the flight.

I retrieved this from Emirates; I have assumed that you live in the US.

There are many different transit without visa (TWOV) concessions, so it is a bit confusing. In the interest of transparency, and because I might have made a mistake, I have included the entire text at the end of the answer. Below is a consideration of each concession.

Because some of the concessions concern transit to a "third country," it's not clear whether they apply when someone is traveling to their country of citizenship. I suspect that the choice of words is poor, and that they do. The following analysis takes that as an assumption.

• The first concession does not apply because you are not flying through URC.

• The second concession does not apply because you wish to leave the airport.

• The third concession:

Passengers with a confirmed onward air, cruise or train ticket to a third country within 24 hours can obtain an entry permit on arrival. They must have documents required for the next destination.

When passengers have obtained an entry permit, they can have multiple transit stops within China (People's Rep.).

This may apply to you. It looks to me like you can go to the airport and apply at the border for an entry permit, which would allow you to go into town and sleep in a hotel, as you have planned. This agrees with the information I found on the web pages of the Chinese embassy in Japan. You should, however, be prepared for the possibility of having to stay in the airport in case of refusal.

• The fourth concession does not apply because you are not flying through SZX.

• The fifth, sixth, and seventh concessions do not apply because you are not flying through any of the named airports.

• The eighth concession:

Nationals of USA with a confirmed onward air, cruise or train ticket to a third country within 144 hours, starting from 00:01 on the day following the day of entry. They must:

-arrive at and depart from one of the following locations: Beijing (PEK), Tianjin (TSN), Shijiazhuang (SJW), Beijing West Railway Station, Tianjin International Cruise Home Port or Qinhuangdao Sea Port; and

-have documents required for the next destination.

This may apply to you, so it may be possible for you to go to your hotel without applying for an entry permit at the border. Again, you should be prepared for the possibility of refusal, in which case you would have to remain in the airport.

• The ninth concession does not apply because you are not flying through either of the named airports.

It looks to me as though the airline, presented with this information, would allow you to board the flight without a visa. If that happens, you would at least be able to take your flight. Whether you will be able to leave the airport and stay in a hotel would still depend on the immigration officer at the passport checkpoint.

The entire text:

Transit - China (People's Rep.) (CN)

Passport
Passport required.

Document Validity:
When in transit, passports and other documents accepted for entry must be valid for a minimum of 3 months from the arrival date.

Visa
Visa required.

TWOV (Transit Without Visa):
Passengers transiting through Urumqi (URC) with a confirmed onward ticket for a flight to a third country within 2 hours. They must stay in the international transit area of the airport and have documents required for the next destination.

• This TWOV facility does not apply when passengers arrive on a direct flight from USA, Guam or Northern Mariana Isl. AND depart on a direct flight to USA, Guam or Northern Mariana Isl..

Passengers with a confirmed onward ticket for a flight to a third country within 24 hours. They must stay in the international transit area of the airport and have documents required for the next destination.

• This TWOV facility does not apply at Fuzhou (FOC), Huangshan (TXN), Mudanjiang (MDG), Shenzhen (SZX), Urumqi (URC) and Yanji (YNJ).

• This TWOV facility does not apply when passengers arrive on a direct flight from USA, Guam or Northern Mariana Isl. AND depart on a direct flight to USA, Guam or Northern Mariana Isl..

Passengers with a confirmed onward air, cruise or train ticket to a third country within 24 hours can obtain an entry permit on arrival. They must have documents required for the next destination.
When passengers have obtained an entry permit, they can have multiple transit stops within China (People's Rep.).

• This TWOV facility does not apply at Fuzhou (FOC), Huangshan (TXN), Mudanjiang (MDG), Shenzhen (SZX), Urumqi (URC) and Yanji (YNJ).

• This TWOV facility does not apply when passengers arrive on a direct flight from USA, Guam or Northern Mariana Isl. AND depart on a direct flight to USA, Guam or Northern Mariana Isl..

Passengers transiting through Shenzhen (SZX) with a confirmed onward air, cruise or train ticket within 24 hours to a third country can obtain an entry permit on arrival. They must have documents required for the next destination. When passengers have obtained an entry permit, they can have multiple transit stops within China (People's Rep.).

• This TWOV facility does not apply when passengers arrive on a direct flight from USA, Guam or Northern Mariana Isl. AND depart on a direct flight to USA, Guam or Northern Mariana Isl..

Nationals of USA transiting through Changsha (CSX), Chengdu (CTU), Chongqing (CKG), Guangzhou (CAN), Qingdao (TAO), Wuhan (WUH), Xi'an (XIY) or Xiamen (XMN) with a confirmed onward ticket for a flight to a third country within 72 hours, starting from 00:01 on the day following the day of entry. They must:
- arrive at and depart from the same airport; and
- have documents required for the next destination.

• This TWOV facility does not apply when passengers arrive on a direct flight from USA, Guam or Northern Mariana Isl. AND depart on a direct flight to USA, Guam or Northern Mariana Isl..

Nationals of USA transiting through Guilin (KWL), Harbin (HRB) or Kunming (KMG) with a confirmed onward ticket for a flight to a third country within 72 hours. They must:
- arrive at and depart from the same airport; and
- have documents required for the next destination.

• This TWOV facility does not apply when passengers arrive on a direct flight from USA, Guam or Northern Mariana Isl. AND depart on a direct flight to USA, Guam or Northern Mariana Isl..

Nationals of USA with a confirmed onward air, cruise or train ticket to a third country within 144 hours, starting from 00:01 on the day following the day of entry. They must:
- arrive at and depart from one of the following locations: Hangzhou (HGH), Nanjing (NKG), Shanghai: Hongqiao (SHA) and Pudong (PVG), Shanghai Port International Cruise Terminal, Shanghai Wusongkou (Baoshan) International Cruise Terminal or Shanghai Railway Station; and
- have documents required for the next destination.

• This TWOV facility does not apply when passengers arrive on a direct flight from USA, Guam or Northern Mariana Isl. AND depart on a direct flight to USA, Guam or Northern Mariana Isl..

Nationals of USA with a confirmed onward air, cruise or train ticket to a third country within 144 hours, starting from 00:01 on the day following the day of entry. They must:
- arrive at and depart from one of the following locations: Beijing (PEK), Tianjin (TSN), Shijiazhuang (SJW), Beijing West Railway Station, Tianjin International Cruise Home Port or Qinhuangdao Sea Port; and
- have documents required for the next destination.

• This TWOV facility does not apply when passengers arrive on a direct flight from USA, Guam or Northern Mariana Isl. AND depart on a direct flight to USA, Guam or Northern Mariana Isl..

Nationals of USA with a confirmed onward ticket for a flight to a third country within 144 hours, starting from 00:01 on the day following the day of entry. They must:
- arrive at and depart from one of the following two airports: Dalian (DLC) or Shenyang (SHE); and
- have documents required for the next destination.

• This TWOV facility does not apply when passengers arrive on a direct flight from USA, Guam or Northern Mariana Isl. AND depart on a direct flight to USA, Guam or Northern Mariana Isl..

Warning:
When passengers transit for a maximum of 144 hours, they can arrive in and depart from any of the following locations: Hangzhou (HGH), Nanjing Lukou (NKG), Shanghai Hongqiao (SHA), Shanghai Pudong (PVG), Shanghai Port International Cruise Terminal, Shanghai Wusongkou (Baoshan) International Cruise Terminal or Shanghai Railway Station. The transit time starts from 00:01 on the day following the day of entry.When passengers transit for a maximum of 144 hours, they can arrive in and depart from any of the following locations: Beijing (PEK), Tianjin (TSN), Shijiazhuang (SJW), Beijing West Railway Station, Tianjin International Cruise Home Port or Qinghuangdao Sea Port. The transit time starts from 00:01 on the day following the day of entry.When passengers transit for a maximum of 144 hours, they can arrive in and depart from any of the following two airports: Dalian (DLC) or Shenyang (SHE). The transit time starts from 00:01 on the day following the day of entry.All transiting passengers are subject to a check by immigration. Passengers in transit must hold passports or other documents accepted to enter China (People's Rep.).

• This does not apply at Beijing (PEK) when passengers stay in the international transit area.

For TWOV through Chengdu (CTU): before departure, a notification must be sent by the carrier to immigration at scbfgj@sina.cn . For TWOV through Changsha (CSX) or Xiamen (XMN) for a maximum stay of 72 hours: before departure, a notification must be sent by the carrier to immigration.For TWOV through Shenzhen (SZX): before departure, a notification must be sent by the carrier to immigration.