Rescue workers scoured Indonesian waters after a ship carrying 59 people capsized in stormy weather, killing at least two children and leaving more than 20 missing, a port official said Thursday.

Crews from a passing oil tanker and fishing boat rescued 33 people in life vests after the KM Wahai Star was pounded by 13-foot waves Tuesday night, said Tumorang Hutasoit, the head of the Ambon Port Authority.

The life vests were handed out minutes before the ship capsized, witnesses said.

"The ship then sank slowly and we jumped into the dark and rough sea," said Nasaruddin, 39, who uses only one name. "We were all panicking, but the crew calmed us down."

He was taken to a nearby island after drifting for 15 hours. His 30-year-old niece was among the missing.

The KM Wahai Star had been on a regular voyage from Buru island to Ambon, the capital of Maluku province, and was carrying 42 passengers and 17 crew. Life vests were handed out by deck hands minutes before the boat sank.

The cause of the accident was unclear, but port officials said a broken engine may have hampered efforts to navigate the storm.

Two children died and authorities were giving up hope of finding the missing, said Karim Tuanaya, acting head of the local port authority. Rescue boats were sent to the area, but heavy rain and story seas were making the search difficult.

Indonesia, the world's largest archipelagic nation, has been hit by a series of sea transportation disasters in recent months. In late December, a passenger ferry sank in a storm in the Java Sea, killing more than 400 people.