Update, 2.21pm The body of a man, believed to be a missing jet ski fisherman, has been found near Shag Island.

"The body of a man has been found this morning near Shag Island, towards the bottom of Waiheke Island," says Inspector Jason Homan

"While formal identification is yet to take place, Police believe the body is likely to be that of the man who failed to return from a fishing trip on his jet ski yesterday.

"Police would like to extend their thanks to everyone who has assisted with the search and our condolences go out to his whānau," says Inspector Homan.

The death will be referred to the Coroner.

Earlier, 11.30am A search operation is underway for a man overdue from a fishing trip at Kawakawa Bay.

The man left on his jet ski from the Kawakawa Bay boat ramp on Saturday, but has failed to return.

"Police will be searching the area today, with the assistance of Police Maritime Section, Police Eagle helicopter and a Coastguard fixed-wing plane," says Inspector Jason Homan.

"Police are asking members of the public on the water in the Kawakawa Bay and Firth of Thames area today to be vigilant and report any sightings of the jet ski, floating debris, or fishing equipment."

Coastguard New Zealand has also asked for help with sightings or information regarding the overdue jetski.

"The jetski has at least 1 POB [person on board] and is described as a 2 person Seadoo black hull, white and gold topsides," says a Coastguard New Zealand spokesperson.

"Anyone who can provide information about sightings is asked to mark down the GPS coordinates and contact Coastguard Radio or call *500," says Inspector Jason Homan.

Information can also be provided to Police on 111 using event number P051789739.