Eight people died after suffocating in a refrigerated truck in central China's Henan province, investigators said.

In a statement released Sunday, a local investigative team said that the eight had been "illegally" transported in the cold-chain vehicle to the town of Hongzhuangyang.

"The driver found eight people suffocating and unconscious in the car," investigators said, adding that they were later declared dead.

The driver and other "responsible persons" are being held by police, the statement said.

The case is under investigation, it added.

It was not immediately clear if the eight were Chinese nationals or foreigners.