A crew member who leapt off a commercial fishing boat with his belongings in a black plastic rubbish bag had to be rescued by a fellow crew member rowing a dinghy with a branch for an oar.

Mike Gorrie, officer-in-charge of Russell police station, said he was alerted to the drama off Northland's coast about 5.45pm on Thursday after two men were spotted in the water.

A commercial long-line fishing boat was off Bland Bay when there was a disagreement between an 18-year-old crew member and the skipper.

Mr Gorrie said the end result was the teenager, from Kaipara, jumped overboard with some of his possessions.

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It is believed he may have been drinking alcohol before the argument with his boss.

They were about 400m off shore but the teen was struggling with the outgoing tide.

A 20-year-old deckhand, from Mangere, in Auckland, realising the dilemma, decided he would also disembark.

Mr Gorrie said the second deckhand was a stronger swimmer and went straight past his mate to shore where he managed to find a dinghy.

However, lacking a set of oars he instead used a branch to propel himself out to the struggling swimmer, who was thought to be in the water for about 40 minutes.

The teenager and his gear were safely delivered to the shore. Seeing that the two crew were safely on the beach, the commercial vessel motored off.

The duo were given a hot shower at the local camp ground and police took them to Russell, where they stayed with a relative overnight.

"Fair play to the guy who wasn't involved in the argument. Out of concern he has jumped in and saved the other guy," Mr Gorrie said.

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"It could have been more serious and even ended with a drowning or one guy suffering hypothermia."

Police are looking for the skipper of the 15m fishing vessel to talk with him about the incident.