The New Zealand Defence Force has joined Fijian authorities in the search for three young Kiribati fishermen who have been missing for more than five days.

Air Commodore Darryn Webb, the Air Component Commander, said a Royal New Zealand Air Force P-3K2 Orion aircraft began its flight from Auckland at 4.30am and was expected to arrive later this morning.

The search area - between the atoll of Maiana and Tarawa - is about 4300km north of Auckland.

"Given the distance to Kiribati, we've decided to start on this task early and maximise the time for the search effort."

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Fiji's Rescue Coordination Centre (RCC) asked the NZDF to help with aerial search and rescue efforts after a local search since Tuesday failed to find the men.

The trio, aged 25, 27 and 30, were last seen leaving Betio Island, the largest town of Kiribati's capital island of South Tarawa, aboard a 4.5m wooden boat about 3am on Monday.

They were expected to return home later that day.

The men had 56 litres of fuel, a bucket of water and 20 buns with them, according to Fiji's RCC.

Fijian and New Zealand authorities will scour 34,300sq km during the search effort.

A local radio station urged nearby vessels to also keep an eye out for the missing men.

The mission echoes one the NZDF was called to on October 18 to help search for three Kiribati fishermen who had been missing for four days.