Most of the videos of the incident posted by eyewitnesses have since been removed from Chinese social media, but some footage still circulating online shows many people lying on the ground being attended to by medics and bystanders.
Some of the victims are apparently unconscious.
Mr. Chen, an eyewitness, told Chinese news magazine Caixin that at least six groups of people had gathered at the stadium for a routine walk when the incident happened.
Groups use a special footpath that runs along the perimeter of the stadium.
Mr Chen said his group had just completed their third lap around the stadium when a car suddenly rushed towards them at high speed, “hitting many people”.
“He was driving in a loop and people were injured in all areas of the treadmill – east, south, west and north,” another eyewitness told Caixin.
The newspaper reports that among the victims there are many elderly people, as well as teenagers and children.
It is not yet clear whether the incident was linked to the high-profile Zhuhai Air Show, which began on Tuesday at a site just 40 km (24 miles) from the stadium. China is showing off its latest military aircraft and attack drones at the show, and top Russian official Sergei Shoigu is expected to attend.
Several entrances and exits to the sports center were closed for the duration of the air show to facilitate “monitoring,” center management said Tuesday.
China has seen a wave of violent attacks on civilians in recent months.
In September, the man moved on a stabbing in a supermarket in Shanghaithree people died and several were injured.
In the same month, a 10-year-old Japanese student died a day after he was wounded outside his school in southern China.
