Most videos of the incident posted by eyewitnesses have been removed from Chinese social media, but some images still circulating online show many people lying on the ground being treated by paramedics and bystanders.

Some of the victims appear to be unconscious.

An eyewitness, Mr. Chen, told Chinese news magazine Caixin that at least six groups of people had gathered at the stadium for their regular walks when the incident occurred.

Groups use a designated walkway that follows the perimeter of the stadium.

Mr Chen said his group had just completed the third lap around the stadium when a car suddenly drove towards them at high speed, “knocking down many people”.

“It drove in a loop, and people were injured in all areas of the running track – east, south, west and north,” another eyewitness told Caixin.

The station reported that the injured included many elderly people as well as teenagers and children.

It is not clear whether the incident was related to the famous Zhuhai Airshow, which started on Tuesday at a location just 40 km (24 miles) away from the stadium. China is showcasing its latest warplanes and attack drones at the show, and Russian official Sergei Shoigu is expected to attend.

Several entrances and exits to the sports center were closed during the air show to facilitate “control,” center management said Tuesday.

China has seen a series of violent attacks on members of the public in recent months.

In September, a man stabbed himself in a supermarket in Shanghai, killing three people and injuring several others.

That same month, a 10-year-old Japanese student died a day after being stabbed near his school in southern China.