An oil tanker undergoing repairs at a shipyard in western Indonesia caught fire early Wednesday, killing 10 people and injuring 21 others, local police said.

The blaze broke out aboard the MT Federal II at around 4:30 am (2130 GMT Tuesday), while the vessel was docked at a shipyard on Batam island, near Singapore, local police chief Zaenal Arifin told AFP.

Sparks were seen inside a storage area of the vessel, he added. The fire was extinguished about an hour later.

The victims were taken to four nearby hospitals, and authorities have launched an investigation into the cause of the fire.

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The Indonesian-flagged tanker was not carrying any oil cargo at the time of the incident, Arifin said, adding that the ship had been emptied ahead of the repair work.

It was the second fatal fire aboard the same vessel in less than five months.

In June, four people were killed in a similar incident, according to Zaenal, which investigators later blamed on sparks igniting residual gas in a storage area that had not been fully cleared.

He said two health and safety workers from the shipyard were named as suspects in relation to the June incident, which occurred in a different part of the vessel.