The black box of a bus which plunged into the Yangtze River in Chongqing was retrieved from the river early Wednesday morning and handed to local traffic authorities for investigation.

Chinese rescuers search for passengers at the accident site after a bus crashed with a car and plunged into the Yangtze River from a bridge, in Wanzhou district, Chongqing, China, October 30 2018. [Photo:IC]

The black box was salvaged around 0:50am and turned to the traffic police, CCTV reported.

The bus fell off to the Yangtze River on Sunday and the death toll has risen to nine, local authorities said on Tuesday.

The rescuers are preparing to salvage the bus Wednesday.

Divers had found nine bodies and retrieved seven of them from the river in Chongqing City as of 4:45pm on Tuesday, according to the rescue headquarters.

Three bodies have been identified while the other four are undergoing DNA analysis.

A probe revealed that 15 people, including the driver, were on board the bus.

The bus veered onto the wrong side of the road and collided with an oncoming car before breaking through road fencing and falling off a bridge in Wanzhou District on Sunday.

With the help of sonar technology and underwater robots, the bus was found 73 meters underwater, according to Zhou Dongrong, from Shanghai Salvage Co, a state-run salvage firm.

But water hazard and limited underwater visibility have hindered rescue efforts.