A dam burst on the outskirts of Jakarta before dawn Friday, sending a flash flood into a crowded residential neighborhood in the Indonesian capital, submerging hundreds of houses and killing at least 50 people, officials said.

Rescuers predicted the death toll would climb, as most people were sleeping when the dam exploded.

The failure of the decades-old dam, which burst at around 2 a.m. local time following hours of torrential rain, completely destroyed some houses and inundated at least 400 others, Health Ministry crisis centre chief Rustam Pakaya said. Floodwaters were up to 2.5 metres deep in some areas, police and witnesses said.

Water levels reached rooftops in some places. Metro TV footage showed several bodies floating amid chairs, clothing and other debris. Telephone lines were toppled and cars swept away, some as far as hundreds of metres.

At least 50 people died, Pakaya said. It is not immediately clear what caused the dam to break.

"A flash flood came suddenly and was horrifying," said Seto Mulyadi, whose car was washed nearly 100 metres from his driveway into a public park. "My house is in a dreadful mess.... Thank God my family is safe."

Mulyadi said he heard a siren sound at the dam before the water smashed out all the windows and doors and inundated his home. His wife and four children were all sleep upstairs and were unharmed, Mulyadi said.

A rescue worker identified only as Toni told El Shinta radio that another 19 people were being treated at nearby hospitals.

It was unclear what caused the failure of the 10-metre-high dam, which was holding back around two million cubic metres of water at the Pesanggrahan River, according to South Jakarta police Chief Makmur Simbolon.