Police have identified a suspect in the incident, according to a post on a verified social media account of state broadcaster CCTV.
The broadcaster posted pictures of the 33-year-old man and personal identifying information, adding that police were “investigating and pursuing” him for his role in “a serious crime.” It did not give any indication of a possible motive.
Later Tuesday, Xinhua reported authorities had taken the suspect into custody.
Earlier, officials in Yinchuan, the capital of the remote Ningxia region where the incident occurred, said only that the bus had “suddenly caught fire” near a public square.
Images of the incident posted online showed the bus completely engulfed in flames and a short video of police in yellow rain jackets gathering around the vehicle’s smoking, charred remains.
A total of 32 people were being treated in hospital, according to CCTV, with eight suffering from “serious injuries.”
In past years, there have been several cases of attacks on Chinese public transportation, especially buses.
In 2013 a suicidal man started a fire on a bus in eastern China that killed 47 people including himself, state media said.