An RNZ Air Force plane has flown out of Auckland to help find missing fishermen in Kiribati.

The Orion aircraft took off at 6am today to help search for two separate fishing boats from the tiny Pacific nation.

Both boats failed to return from fishing trips over the weekend, the Air Force said.

The Orion was expected to reach the search area, 4085km north of New Zealand, at midday, Air Component Commander Air Commodore Tim Walshe said.

One of the missing boats was a 6m wooden boat with three people on board, he said.

The second vessel was a 4m canoe with one person on board.

The Fiji Maritime Surveillance Rescue Coordination Centre, which is responsible for the search area, requested help from the NZ Defence Force on Sunday.

A local patrol boat had earlier failed to find the boats on Friday.

They were last seen by a local search aircraft late on Friday afternoon.