According to preliminary investigations, the fire was caused by a 40-year-old driver surnamed Chen who was smoking a cigarette inside the vehicle, the Shanghai public security bureau said on its official Weibo feed.
Chen, who is currently receiving treatment, is suspected of illegally transporting dangerous substances, police said.
The Shanghai government said in a short statement the vehicle hit the pedestrians on a road running next to People’s Square, injuring 18 people, three of them seriously.
Shanghai-based news portal The Paper said the vehicle was a minivan, and cited eyewitnesses as saying it was on fire as it drove onto the pavement, knocked people down and came to a stop in front of a Starbucks outlet.
A Shanghai-based Starbucks spokesman told Reuters the store was not damaged and its customers and employees were safe.
“The store is currently closed and we will assist the authorities in their investigations,” he said.
The incident coincides with a visit to the city by British Prime Minister Theresa May.
Some bystanders tried to break the window of the vehicle and drag out the six people in the vehicle, including the driver, The Paper reported in a story later reposted by the official People’s Daily newspaper.
Other witnesses told the news outlet that there were gas cylinders in the vehicle.
Footage on Chinese social media, which Reuters could not independently verify, showed smoke coming out from the vehicle and people lying flat on the ground injured in the street.