Rescuers have discovered the charred remains of at least seven people a day after a series of explosions aboard an Indonesian oil tanker, and police said Tuesday the toll could rise.

The dead were among dozens trapped on the 250-metre (820-foot) Jag Leela when it burst into flames after several explosions at North Sumatra's Belawan port, one of the country's busiest.

Firefighters aboard another boat battled for hours to extinguish the inferno on the Indonesia flagged vessel, which was docked for repairs. "The deceased were among those trapped during the blaze. They didn't find a way out," said local police spokesman MP Nainggolan.

DNA tests were being performed to identify badly burned victims, and some crew were still missing, he added. The blaze injured at least 22 people. The cause of the explosions and fire was not yet known, authorities said.

Tina Siregar said two of her brothers may be among the dead. "Both of them were working to repair the tanker," she said. "They were on board when this happened."