Kiwi rescue officials have helped save the lives of four fishermen found cold and huddled together on the hull of their capsized boat.

Rescue Coordination Centre NZ organised the rescue of the men, whose CFV Salvation capsized at 3am this morning in large swells, 25 nautical miles North East of American Samoa.

The stricken group perched on the 10m fishing vessel's upturned hull and huddled together in the cold until daybreak.

In the morning light, the catamaran's owner swam under the capsized vessel and retrieved its emergency position indicating radio beacon (Epirb) which he then set off.

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The centre received the locator beacon alert from the vessel at 7am today and began working closely with local rescue services and directing them to the location.

A police patrol boat from Pago Pago, which was carrying out training at the time, responded to the request and was on the scene in 45 minutes.

They found the people in the water and returned them safely to land.

All four were in good health.

"The [patrol boat] was already on the water and ready to respond so that certainly cut down the response time," search and rescue officer Drew Coleman said.

"If they weren't already on the water then we would have requested them to respond and they would have had to prepare their vessel and crew before heading out."

Coleman said the lesson from the incident was that boat owners should consider registering a float-free Epirb if they didn't have one.

"They detach when boats sink and alert rescuers to your location. These people had also registered their beacon.

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"It meant that when we received their alert we knew key details – such as who owned the vessel and their contact details – that helped us speed up this rescue and save their lives."

Coleman said there were several hundred beacon activations every year and each was treated as a worst-case situation.

"Unless we can actually contact the vessel via radio or cellphone, we don't actually know what's going on until we get to the scene."

Rescue Coordination Centre NZ is responsible for a search and rescue region which covers 30 million square km stretching from Antarctica almost to the equator.