Searchers are back out on Lake Rotoiti this morning, five days after a 48-year-old went missing.

Rotorua constable Colin Fraser, from Search and Rescue, said police dive squad members, the Navy, police staff and Coastguard were among those searching for the man's body today.

The Aucklander went missing after jumping off a boat on the lake on Wednesday about 2pm.

The man, described by his brother as a strong swimmer, jumped off a boat to retrieve his hat when it blew off.

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His lifejacket came off and he drifted away from the boat, from which his partner and 9-year-old son were unable to get to him.

Mr Fraser said the navy had brought in an underwater sonar device on Saturday, which was being used to identify targets for the police divers.

He said between the navy and police there were about 12 people involved in the search, as well as five from Coastguard, a couple of boats from the Harbourmaster and the BayTrust Rescue Helicopter's small rubber boat.