A North Korean ship has reportedly sunk in waters off Japan.

A source from Japan's maritime authorities said the Chongbong, a 5,500-ton freighter, sank in waters off Shimane Prefecture in western Japan at around 2:32 p.m. on Saturday.

Yonhap News reported that the vessel appeared to have been on its way to Songrim Port in North Korea's southwestern Hwanghae Province after leaving Chongjin, a port in its northeastern region.

The ship was said to be carrying some 6,500 tons of iron.

All 21 crew members on board were rescued by a North Korean oil ship passing nearby, according to the source.

A North Korean vessel named "Chongbong" is included in a United Nations Security Council sanction list, but it has yet to be confirmed whether they are the same ship.