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 China Daily reports.
Passengers can be heard screaming in the disturbing footage, shared by Chinese state media.
Police said the passenger, identified as a 48-year-old woman with the surname Liu, was angry that the bus had missed her stop.
They said she hit the driver, named Ran, with her mobile phone when he refused to stop and let her off.
Witnesses had said they saw the bus swerve across to the wrong side of the road before crashing through a safety barrier in Wanzhou district.
A huge rescue operation was mounted with teams of divers and dozens of boats and cranes deployed. But there have been no reports of survivors.
The wreckage of the bus was pulled out of the river from a depth of 71m on Wednesday night. Several of the passengers’ bodies had to be retrieved by divers.
The crash, on well-maintained and relatively quiet bridge, has shocked China.
Social media comments on Friday widely blamed the passenger for the crash, though some also criticised the driver for reacting.
One poster on Weibo, Wanten888, said: “If we see any passenger quarrelling with bus driver, we shouldn’t stay quiet!”
Another said it was “heartbreaking” to hear the terrified passengers, while a Weibo user called Liza said there should be a law banning passengers from distracting bus drivers.