The bus plunged 50m (164ft) off a bridge into the Yangtze River in Chongqing on Sunday – at least 13 people died and two more are missing.
Early reports said the bus had swerved to avoid an oncoming vehicle.
But the new footage shows the driver was being hit by a passenger and then struck her back.
The bus, travelling at speed, then turns into the opposite lane and smashes through the safety barriers, before the footage cuts out.
Police have said the fight was the cause of the crash, state newspaper People’s Daily reports.
Passengers can be heard screaming in the disturbing footage, which has been shared by the Chinese state media.