A ferry with an estimated 50 people on board has been missing for more than a week off the coast of the Pacific nation of Kiribati, rescue authorities say.

New Zealand's Rescue Coordination Centre said it had sent a military Orion plane to assist in the search of an area of ocean approximately the size of Britain. The search is being led by Fiji.

The NZ Air Force said it searched more than 300,000 square kilometres on Saturday and found nothing.

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Authorities said the ferry departed Nonouti Island bound for the Kiribati capital of South Tarawa on January 18.

The 240-kilometre journey was expected to take two days.

NZ senior search and rescue officer John Ashby said the MV Butiraoi, a 17.5-metre wooden catamaran, was first reported missing to them late Friday (local time).

He said the vessel underwent repairs to its propeller shaft just before leaving, which may have contributed to navigation problems.

Ashby said people on islands and vessels along the planned route are being contacted to ask if they have seen the vessel.

Kiribati is a remote, impoverished nation of 33 atolls that is home to about 108,000 people.

NZ's search for the ferry was wound up about 5:00pm Saturday (local time) and was scheduled to resume at first light on Sunday.

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AP