Police and the Air Force are searching for a small boat missing off Northland's east coast that's thought to have 700kg of methamphetamine on board.

Detective Superintendent Greg Williams, director of the National Organised Crime Group, said police had serious concern for the missing vessel and its occupants.

The missing boat is believed to be a 3.5-metre skiff with two people on board.

Williams said two failed attempts were made by shore parties to rendezvous with the boat, which was last seen about 50 nautical miles, or almost 100km, off the coast northwest of the Bay of Islands.

The drug-importation attempt was being investigated as part of Operation fantail, which had so far led to 10 people being arrested in Northland and Auckland.

They had been charged with conspiracy to import a class A drug and participating in a criminal organised group.

All 10 had since appeared in court, with nine remanded in custody and one currently on bail ahead of further appearances over the coming months.

Twelve search warrants were executed during the operation, which led to police locating about $130,000 in cash, two rifles, four handheld GPS units and two satellite phones.

A small quantity of class C controlled drugs and cellphones were also seized.

Williams said Operation Fantail was investigating a transnational organised crime group, who were believed to be facilitating the importation of 700kg of methamphetamine into New Zealand by sea.

The case has some similarities to a bungled drug smuggling attempt in 2016 when almost half a tonne of methamphetamine was landed on Northland's Ninety Mile Beach.

The Auckland-based drug importers were sentenced to lengthy prison terms and the stranger-than-fiction saga spawned a TV series named Far North.

This story was originally published by RNZ