Photo: Screenshot of China Central Television

A bus carrying an unspecified number of students crashed into a local reservoir in Anshun, Southwest China's Guizhou Province on Tuesday, the first day of the college entrance exam, killing at least 21. 

As of press time, 37 people have been found, among whom 16 got injured, 20 died and one was confirmed dead after being sent to the hospital. Twelve of the 37 people are students and five of them were dead, said local authorities.

The bus was refloated and the driver was found dead. The rescue is ongoing. The Ministry of Public Security has sent a team to the site to investigate the incident. 

Eighteen passengers from the bus have been rescued and sent to hospitals for treatment, of whom two have died, Guizhou Daily reported. The exact number of casualties is not known, and local authorities are working to rescue more victims. 

The passengers included senior high school students who were about to sit the life-changing college entrance examinations, or gaokao, China Central Television (CCTV) reported.

A piece of video footage, which was taken from a roadside monitoring camera and released online, showed that the bus travelled slowly on the road around noon12:17. It suddenly veered left, crossed the road, broke the barrier guardrail and fell into the reservoir. 

According to photos and videos circulated online, the blue bus was pulled out of the water at around 3 pm after it hit the guardrail of the road and sank into the water at noon. The bus had no passengers in it when it was pulled out. 

A local resident told the Global Times that she was in a library when she heard ambulance sirens, which were so loud that they could be heard across the city. 

Nearby roads were closed to traffic when she arrived at the scene at around 1 pm, and firefighters, police and medics had arrived to help with rescue efforts, she said. She heard that there were senior high school students who were about to take the college entrance examinations on the bus, but she did not know the exact number or the details of their conditions. 

Ministry of Transport urged public transport companies to pay close attention to the mental and physical conditions of drivers after the incident.