An Indonesian ferry with more than 250 passengers on board sank in rough waters off Sumatra island on Sunday, killing at least 29 people, the police said.

So far, the Indonesian rescue workers have saved at least 240 people. They can not give an exact number on how many more passengers may still be in the water because not all of them were registered on the manifest.

The Transport Ministry reported that 292 people were aboard the 270-capacity ship called Dumai Express 10. The vessel left from Batam Island and was on its way to Dumai in Sumatra when the tragedy happened.

A spokesman for the Indonesian Search and Rescue Agency, Gagah Prakoso said, “People are able to survive for around three days at sea so we’ll keep on looking as long as the weather is clear.”

Overcrowded ferries are not something new to the Indonesians. There have been several ferry accidents in the past, and it is common for some passengers’ names to not turn up on the ship’s manifest. Some of the passengers of the Dumai Express 10 did not even have tickets at all.