The Royal New Zealand Navy has joined the search for a man missing off the coast of the Bay of Plenty.

Police were alerted at 11.20pm last night that a 24-year-old man from Rotorua was missing.

The man was one of three people who had gone out fishing in a 14-foot aluminium boat, which overturned.

The others, a 28-year-old man and a 10-year-old boy, were found alive by another fisherman after being washed ashore.

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The man and boy were treated by ambulance for hypothermia and taken to a hospital.

The Westpac helicopter from Auckland and a helicopter from Tauranga are helping with the search.

They are joined by three Coastguard vessels and a Coastguard plane, Surf Life Saving boats, and HMNZS Taupo in searching the open ocean.

Surf Life Saving teams are helping with shoreline searches.

The Police Eagle helicopter, which was used in the search overnight, has returned to Auckland.

The water has flattened out this morning after a night of swells