An additional 13 people have been left injured after the bus plunged down a steep ravine and landed in a river, according to the BBC. At least 25 people have been confirmed as dead.
Some 37 passengers, including a driver, were onboard the bus when the horrific accident happened in South Sumatra province.
Authorities have deployed 120 rescue workers to help survivors and retrieve the dead.
The exact cause of the bus falling into the ravine is currently being investigated.
The bus left Bengkulu city on Sumatra Island earlier on Monday.
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According to local media, it was travelling to the city of Palembang, which is several hours away.
The accident happened at the Liku Lematang area at around 11.15pm local time (4.15pm GMT).
Pager Alam Police chief, Dolly Gumara, said police were currently prioritising evacuating survivors.
He called for victims’ families to travel to the hospital in order to identify their loved ones.
Roads around the site of the accident have been closed and will remain closed.
Police say they have issued warnings to motorists.
Mr Gumara said: “It crashed into the concrete road barrier before plunging into the ravine. Some people are still trapped inside the bus.”
Reports suggest that some people may have been picked up by the bus on the way, making the final passenger count far larger than what was initially thought.
On this, Mr Gumara said: “Some passengers were probably added along the way so there’s a possibility some more people are still missing in the river.”
Traffic accidents are common in Indonesia, where vehicles are often old and poorly maintained and road rules are regularly flouted.
In September, at last 21 people died when a bus plunged into a ravine in West Java’s Sukabumi region.