Fijian authorities have released dramatic photos of the moment a crewman was saved after what is being described as a violent and horrific incident at sea.

A lone man can be seen in a life-raft wrapped in what appears to be a white sheet.

As members of the Fijian Navy pull the life-raft closer to their own ship, the man is pictured wearing just a pair of shorts and his arms wrapped tightly around himself.

The rescue comes as authorities in the area investigate an incident on board a fishing vessel that was so horrific it prompted up to six crewmen to jump overboard.

The Fiji Times reported that local authorities were investigating claims of an alleged beheading on board the Fijian-flagged FV TIRO II earlier this week.

Navy commander Captain Humphrey Tawake told the newspaper authorities would reveal more in due time.

"The vessel's crew are Chinese, Indonesian and Fijian nationals and we are aware of the allegations that a Fijian national had beheaded a second Fijian national following a heated argument," he said.

The Royal New Zealand Air Force was called on to help in the search for the missing crew members.

A lone man is spotted in a life-raft by members of the Fijian Navy. Photo / Rescue Coordination Centre Fiji

An aircrew on a P3 Orion aircraft located the vessel involved - named as the Fijian-flagged FV TIRO II - about 90 nautical miles west of the island nation.

A Royal NZ Air Force spokesman told the Herald yesterday they too were told of reports of an alleged violent incident that happened on board.

"The boat crew reported that on Monday night, six crew members abandoned the vessel.

"One person was aboard a life-raft ... the other five entering the water without lifejackets."

A survivor is picked up by members of the Fijian Navy. Photo / Republic of Fiji Navy

The Kiwi aircrew carried out a search for the life-raft - which they found afterwards and alerted Fijian authorities, who sent out a vessel to pick the man up.

Five others remain missing at sea

Five other crewmen - two Fijian locals and there Indonesian nationals - remain missing, however.

Search efforts were hindered yesterday after the weather deteriorated the night before.

In an update last night, a statement from the Rescue Coordination Centre Fiji said another two crewmen - who stayed on board the fishing vessel - were picked up yesterday morning by another fishing vessel in the area.

Authorities are working to get those two crew members to police for questioning.

The TIRO II is said to have sunk yesterday morning after taking on water the previous night.

The man in the life-raft has since been transferred to local police for questioning.

"Information regarding what transpired onboard that led to this tragic incident will be investigated by the police," a statement from the Fijian coordination centre said.

"The survivors will be taken in for questioning after being cleared by health officials."