The altercation allegedly confused the driver, causing the bus to crash into a barrier on the R59, near Meyerton in the Vaal Triangle, before plummeting into a stream next to the highway.

Gauteng traffic police inspector Albert Tsubella said one of the 55 survivors of the accident - who were all injured - said the bus, travelling from Sebokeng to Henley-on-Klip, took a different route from what it usually took, to avoid a service delivery protest in Sebokeng, where protesters were allegedly stoning vehicles.

Tsubella said the driver - who was also killed in the crash - became confused by passengers chanting which route he should take first.

"The driver was either speeding or applied the brakes too late, or the brakes failed. This caused the bus to crash through a barrier into the ravine," said Tsubella.

Police suspect some passengers anticipated the danger when the bus went out of control.

"A man's finger was found on the bridge and his body was found under the bus. We suspect he tried to escape," said a police officer at the scene.

According to police spokesman Captain Shado Mashobane, paramedics saw a hand sticking out from beneath the bus as they were removing bodies and survivors.

"Four people were found trapped there. They seem to have been the first ones flung out."

Thirteen women and six men, including the bus driver, were confirmed dead at the scene by paramedics.

A woman who suffered serious injuries was airlifted, to Chris Hani-Baragwanath Hospital in Soweto, along with a paramedic suffering from exhaustion, who was taken to Vereeniging Medi-Clinic.

The rest of the survivors were taken by ambulance to the Sebokeng, Natalspruit and Kopanong hospitals.

"There were no children among the passengers on the bus, only adults on their way to work," said Putco spokesman Raphiri Matsaneng.

He said the bus had passed a roadworthy test on June 14 this year.