Six people in a small boat missing amid rough seas in Fiji have been rescued by a Royal NZ Air Force crew.

The group had left Namuka Island for Fulaga in the Lau Group in a small boat on Thursday morning but failed to reach their destination, the NZ Defence Force said.

The RNZAF P-8A Poseidon crew were about to carry out a fishery patrol in the island nation when the Joint Rescue Coordination Centre Fiji requested help searching for the vessel.

An initial search was carried out by local vessels before a chartered local aircraft and the RNZAF joined efforts on Friday.

"The weather was challenging with strong winds and 3.5m swells creating salt spray which decreased visibility," No. 5 Squadron tactical coordinator and crew member Flight Lieutenant Holly Graham said.

After six hours of searching, the vessel was spotted by the Air Force crew in fading light around 5.30pm, 14.6 nautical miles southwest of Vanuavatu.

The Air Force crew radioed the nearby Republic of Fiji Navy Ship Savenaca and sailed to rescue the group shortly after 8pm.

The group were taken to Suva for medical assessment before being reunited with their families and loved ones.

"It was a long day, but the crew was delighted with the outcome. Our thanks to all who assisted, particularly the crew of RFNS Savenaca. Our best wishes to the survivors and their families," Graham said.