TOKYO — A cargo ship broke into two pieces after running aground in a northern Japanese port and is spilling oil into the sea, Japan's coast guard said Thursday.

All 21 Chinese and Filipino crew members were safely rescued by the coast guard, said the ship's Japanese operator, NYK Line.

The 39,910-ton wood-chip carrier Crimson Polaris went aground Wednesday while sailing inside Hachinohe Port. It managed to free itself from the seabed, but suffered a crack which widened and eventually caused the vessel to split into two early Thursday, the coast guard said.

Officials were trying to contain the oil spill. The amount of oil leaked is under investigation, NYK Line said in a statement.

The broken hull of the Panamanian-registered ship has drifted about 4 kilometers (2.4 miles) off the coast, it said. (AP)