A New Zealand Air Force search plane has helped to seize more than five tonnes of hashish from drug traffickers off the coast of Somalia.

The $313 million drug haul was part of an international counter-piracy operation involving an RNZAF P-3K2 Orion aircraft.

The New Zealand plane and an Australian Anzac class frigate, the HMAS Toowoomba, battled bad weather as they trailed a dhow -- a type of sailboat -- from the Arabian Sea to the Horn of Africa.

After four days, the crew of HMAS Toowoomba was able to board the dhow. An exhaustive search uncovered 5.59 tonnes of hashish in hessian bags.

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New Zealand Defence Force air component commander Air Commodore Kevin McEvoy said: "This was a great result for the combined New Zealand and Australian force and our Pakistan Navy colleagues at CTF-150, who led the operation.

"We often work with other nations on operations and it is good for our people to be involved in a large-scale operation that can make a real difference."

Air Commodore McEvoy said the P-3K2 was regularly used to conduct a wide range of maritime surveillance work, and its crew was highly skilled and able to contribute their expertise to the task force.

HMAS Toowoomba boarding officer Lieutenant Stefan Stuart said the drugs were well hidden and, once found, were extremely difficult to access and remove.

"It is great to make an intercept of this magnitude. The weather was not on our side but our training and our persistence paid off."

The operation was conducted under the command of the Combined Task Force 150 (CTF-150), which is part of the Combined Maritime Forces.

The international task force carries out maritime security operations with the aim of preventing terrorists from using the seas to launch attacks or transport personnel, weapons or other illicit material.

The drug haul was its first successful counter-narcotics operation since the Pakistan Navy took command of the maritime security and counter-terrorism mission in August.

Task force head Commodore Sajid Mahmood, of the Pakistan Navy, said he was "incredibly proud" of the sailors and airmen involved in the complicated operation.

"CTF-150 has a long history of disrupting narcotics trafficking in the region and Toowoomba, with the support of 5 Squadron of the RNZAF, have carried this on. Keep up the good work!"

The New Zealand personnel and aircraft on the task force are due to be replaced by a P-3K2 and an RNZAF 757, which would leave New Zealand in mid-October.