The death of a 33-year-old father of four at Port Nelson on Saturday morning has left his workmates devastated.

The Nelson man fell from the deck on the MJ Souza where he was working, through an open hold, police say.

Police, colleagues and St John Ambulance paramedics tried to resuscitate the man but he died at the scene.

The fishing vessel is operated by Talleys Group.

Talley's deep sea division chief executive Tony Hazlett told the Nelson Mail they're devastated by the accident and an investigation is underway.

"Our thoughts at the moment are immediately with his partner and four children.

"The crew is very, very close-knit. There is a crew of 20 on the vessel who live, work, eat and sleep together. That vessel is their home," he said.

"We are devastated by this. We are going to find out what happened and why."

The man had worked for the company for about four years and he was a respected employee, Mr Hazlett said.

Police and Maritime New Zealand are also investigating the accident.

The MJ Souza is based in the western and central Pacific for most of the year and during the summer it fishes for skipjack tuna in New Zealand, according to the company's website.