CHENGDU - The death toll from a road accident on Sunday in Southwest China's Sichuan province has hit 21, local authorities said on Monday.

The accident occurred at 2 pm in Zhenwu village in Quxian county, Dazhou city, when a passenger bus collided with a heavy-duty truck loaded with sand and cobblestones. The bus plunged into a three-meter-deep riverbed, the Quxian county's publicity department said in a statement.

The bus -- which had 24 people on board, including 12 students -- was then buried by sand and cobblestones from the overturned truck.

Of the 25 people including the truck driver, 16 were killed at the scene, and another five people died after failed medical treatment, the statement said.

The cause of the accident is under investigation.

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Firefighters search for survivors at a road accident site in Zhenwu village, Dazhou city of Sichuan province, September 15. [Xu Taiyuan/Asianewsphoto]