A bus carrying students and teachers returning from a graduation celebration crashed in Subang, Indonesia, on Saturday evening, killing at least 11 people, many of them students.

The crash occurred around 6:45 p.m. as the vehicle was returning from a hilly resort area in Bandung to Depok, West Java, the authorities said.

While the cause of the accident was still under investigation on Sunday, the West Java police said that the bus had sped out of control on a downhill road and crashed into multiple vehicles. An initial investigation revealed that the bus was apparently not fit for the road and had malfunctioning breaks.

There were 61 passengers aboard, according to the police, who said that nine people died at the scene and two died later in a hospital.

Among the dead were several students, a teacher and a motorcyclist. Dozens of others were injured and hospitalized, some in critical condition.

Eighteen surgeries for serious injuries have been carried out so far, a West Java police commissioner said on Sunday in a news briefing.

A local television broadcast ran video showing the overturned bus with its windows shattered and frame severely battered.

Road accidents involving multiple fatalities are not uncommon in Indonesia, where hilly terrain and inadequate road lighting cause hazardous driving conditions that lead to regular crashes.

Three years ago, a bus crash killed 29 people, including middle school students who were on their way home from a school trip. Police investigations cited malfunctioning breaks in that accident. In 2019, another bus crash killed 35 people when the vehicle fell into a 262-foot ravine.