The incident occurred on July 11 at Caojiabao International Airport in Xining City, Qinghai Province, as passengers of China Eastern Airlines flight, scheduled to depart for Xi'an, were being transported by bus to the aircraft, Sinchew Daily reported.
After all passengers had boarded, the driver closed the doors, with the air conditioning system turned off.
The driver then unexpectedly left the vehicle and took the key with him for unknown reasons, according to Sina News.
Trapped in the stifling heat, many passengers reported feeling dizzy, struggling to breathe, and panicking. Some broke the windows with emergency hammers to let in fresh air.
Only after the windows were broken did the driver return and turn on the air conditioning.
An ambulance was dispatched shortly after to care for the passengers. The incident delayed the flight by more than 30 minutes.
A female passenger was taken to an emergency room. Her condition was not serious, and she was rebooked on a flight to Xi'an the following day.
A representative of Caojiabao Airport confirmed that the incident was under investigation.