A father and son survived hours in the water before swimming to an island after their boat capsized in the Firth of Thames overnight. 

They were found standing at the southern end of Ponui Island at 12.23am, more than six hours after their boat sank. 

Coastguard NZ said they were cold, but unharmed, and their lives had been saved by wearing life jackets. 

The two men left Kawakawa Bay to the west of the Firth of Thames in a three-metre dinghy at 3pm yesterday. 

They were reported missing by a family member shortly after 11pm after they failed to return as expected at 8pm. 

A late night rescue from Police Deodar III and Maraetai Rescue One used night vision and large spotlights to scour the area around Pakihi Island and the Sandspit passage, before the pair were found on Ponui Island. 

Maraetai Rescue One provided them with warm beanies and jerseys and took them back to shore. 

Coastguard Maraetai skipper Trent Dixon said both men were wearing lifejackets, similar to the ones he and his Coastguard unit wears, which undoubtedly saved their lives. 

"This was a fantastic result considering how long they were in the water for," he said. 

"We received excellent information from the informant about where they were heading and what equipment they had on-board. 

"Working seamlessly together with Maritime Police, we are delighted to be able to bring the pair home after a long period in the water."