One person has been taken to hospital after a boating drama on Auckland's Waitemata Harbour this morning.

Three people had to swim for it near Waiheke Island this morning, when their boat started taking on water.

The vessel went down so quickly their marine radio was submerged before they could get to it.

Emergency services were alerted by a mayday call from a cellphone, reportedly from a female occupant of the boat.

The police launch Deodar and the Waiheke Island ferry were employed in the search.

A rescue helicopter and several civilian boats were also reported to be assisting.

It was the second rescue on the harbour this morning.

Another boat was run aground at Waiheke after it began taking on water.