At least ten people were killed and 21 others injured when an oil tanker caught fire early Wednesday at a shipyard on Batam island, near Singapore, police said.

The blaze broke out aboard the MT Federal II at around 4:30 a.m. (2130 GMT Tuesday) while the vessel was docked for repairs, according to local police chief Zaenal Arifin.

Sparks were seen inside one of the ship’s storage areas before the fire quickly spread. It took firefighters about an hour to bring it under control.

The victims were taken to four nearby hospitals, and investigators have launched a probe into the cause of the incident.

The Indonesian-flagged tanker had been emptied of oil cargo ahead of the repair work, Arifin said.

It was the second deadly fire on the same vessel in less than five months. In June, four people were killed in a similar incident, later traced to sparks igniting leftover gas in a storage compartment.

Two health and safety workers from the shipyard were charged in connection with that earlier blaze, which occurred in a different section of the ship.