At least 18 people died when a passenger speedboat carrying 96 Indonesian workers capsized on Wednesday.

The boat, from Johor, Malaysia, sank off Indonesia’s Batam island at about 5 am, when it was hit by big waves in stormy weather. Sambudi Gusdian, the island police chief, said that searches had rescued 39 people alive so far.

Police spokesperson Airlangga said, “Search and rescue efforts continue to find the rest of the passengers.”

A 51 year old survivor, Haryanto said the boat capsized amid heavy rain and high waves about two hours after it left Johor Bahru in Malaysia. He also said the boat was overcrowded.

He said, “It was so crowded, some of us could not sit.” He was saved by fishermen after swimming for about two hours. Like many Indonesians, he goes by one name.

More than a dozen boats and a police helicopter are involved in the search and rescue effort.

Police suspect that the trip was illegal and the workers were undocumented becauase of the high fares that passengers said they paid.

Gusdian said that an Indonesian woman believed to be responsible for the voyage, was arrested as she tried to leave Batam for Singapore.

Speedboat and ferries are common form of transportation in Indonesia, a sprawling archipelago. Sinking is common due to poorly enforced safety regulations.

In 2009, one of the worst ferry sinking in recent years took place in Sulawasi, killing more than 300 people.