A cargo ship collided with a chemical-laden tanker off South Korea's southeast coast early Sunday, causing the tanker to catch fire, but all 91 crew members on the two vessels were rescued safely, coast guard officials said.

The 55,000-ton freighter Gravity Highway was on a test-run when it collided with Maritime Maisie, a tanker carrying 29,337 tons of inflammable chemicals, in waters about 9.2 nautical miles off the southeastern port city of Busan around 2:15 a.m., officials said.

The impact caused a fire on the tanker, which was carrying 27 crew members.

Sixteen coast guard boats, some Navy vessels and helicopters were sent to the scene, and rescued all crew members aboard the tanker, officials said. Firefighters brought the blaze under control around 10 a.m. and were trying to put it out completely, they added.

Some crew members of the tanker sustained light burns or abrasions, officials said.

About 4,000 tons of chemicals paraxylene and acrylonitrile were lost from burning, but the fire did not spread to other containers, officials said. They said no chemicals were released into the sea and the tanker is unlikely to sink.

The freighter, which was carrying 64 crew members, also caught fire that was extinguished shortly. It was being towed to a shipyard near the scene, officials said.

Officials said they were investigating the exact cause of the collision. (Yonhap News)