Waikato police are liaising with Interpol in the disappearance of Alan Langdon and his daughter.

Police are looking at a multitude of possible scenarios as part of the search, including advising and liaising with Interpol, in the event Alan has left New Zealand.

Extensive search activity has been under way since police were notified on December 27 Alan and Que were missing.

A Philips Trust Air Rescue fixed wing plane has searched from Mokau to Port Waikato, including harbours and coastline, out to six nautical miles.

An Airforce P3 Orion has searched the western coastline from Kawhia to Cape Reinga and the eastern coastline to the Bay of Islands, out to 35 nautical miles.

Coastguard air patrol have searched and continue to search the bays and harbours on both coasts of Northland. Coastguard units have also searched Hokianga and Houhora Harbours.

Maritime NZ continue to broadcast police interest in the catamaran on marine channels.

The focus of the search effort is currently in the Northland area, as police have received sightings of a vessel similar to Alan's heading in that direction over the last few days.

The 21-foot catamaran is un-named but has the number T878 on the sail. It is a wooden Tiki 21, Wharram vessel, coloured white with blue anti-foul below the water line. It has been modified with a Bermuda mast.

If you believe you have seen the vessel in the last few days, or you think you may have information which would assist the search effort, please contact your local police station.