Moscow: A shark attacked a young man in the Russian Far East biting off his arms in an extremely rare attack in the northwestern part of the Sea of Japan, a report said on Wednesday.

"A 25-year-old man was brought in in grave condition, unconscious. His arms were chewed off at the elbows," the Interfax news agency quoted a source in a hospital in the Khasan district of the Far Eastern Primorye region as saying.

"He'll live," the source added.

A local law enforcement source told Interfax that a shark attacked the man 50 metres off the shore earlier Wednesday. "A witness helped the victim to get out of the water and also called rescue workers and medics," it said.

A spokesman for the local branch of the emergencies ministry confirmed to AFP that a "sea animal" attacked a man in the southern Khasan region but declined to provide further details.

Another local spokesman said officials expected to receive more details of the attack after hoping to speak to the man on Thursday.

Following the attack, local emergencies ministry officials toured the area warning thousands of swimmers to watch out for sharks, Interfax said.

Several types of sharks including the herring shark can be spotted in the northwestern part of the Sea of Japan but they do not attack people and swimming there is considered generally safe.

The emergencies ministry spokesman told AFP his ministry has never before registered a shark attack on a human in the Primorye region.