The death toll of a fatal bus accident in Indonesia's South Sumatra province two days ago rose to at least 35, according to local media reports on Thursday. 

The bus was carrying dozens of passengers and careered into a 150-meter (500-foot) ravine in a remote and steep area near the town of Pagar Alam in South Sumatra Province just before midnight (1600 GMT) on Monday and ended up in a river, local police spokesman Dolly Gumara told AFP. 

He said the bus crashed into a concrete road barrier before the plunge and some people were still trapped in the bus.

According to the country's Antara news agency, there were 37 people aboard when the incident happened and 13 were seriously injured.

However, some survivors told the police that around 50 were inside.

"Some passengers were probably added along the way so there's a possibility some more people are still missing in the river," Gumara said. 

Rescuers were scouring the river and nearby slopes for victims.

The cause of the incident is related to brake failure, the reports said. 

(With input from AFP, Xinhua)