Maritime authorities are investigating the death of a Nelson crewman on board a fishing longliner due at Port Nelson tomorrow.

It is understood the man died as the result of an accident on board the Antarctic Chieftain on Sunday in international waters as it voyaged towards Nelson. His name has not been released.

The Antarctic Chieftain operates part of the year for New Zealand Longline, a joint venture between Sealord and Talley's, catching toothfish in the Ross Sea.

It is returning from a charter to Australian Longline, a Sealord joint venture with its Japanese co-owner Nissui, and has been operating in the Australian Heard and Maquarie Island fisheries.

In a statement, Australian Longline chief executive Les Scott said senior Sealord staff in Nelson were spending time with the crew member's family, "supporting them in any way they can".

Support was also being provided for the crew members on board the ship.

"Out of respect for his family and to give them the opportunity to grieve privately the companies have chosen at this time not to release the crew member's name."

Mr Scott said the circumstances leading to the man's death, and the cause of death, were unknown, and would be investigated.

Because the ship was operating under the Australian flag and outside New Zealand territorial waters when the death occurred, the Australian Maritime Safety Authority is leading the official investigation.

Maritime New Zealand spokesman Steve Rendle said the Australian agency was sending a representative to Nelson, and the New Zealand Police were also looking into the death on behalf of the coroner, with Maritime New Zealand available to assist if required.

- © Fairfax NZ News