Four men have been rescued after their boat capsized crossing the Kawhia bar this morning.

Coastguard New Zealand said the alarm was raised at 6.48am when the 5.3m Haines Hunter failed to report it had safely crossed the bar.

One man was plucked from the water by a passing vessel, two swam ashore and one man was found clinging to a rock.

Everyone on the stricken vessel was now safe.

Coastguard NZ spokeswoman Monique Caddy said when the boat failed to report a successful bar crossing after 20 minutes the alarm was raised at the Coastguard operations centre.

There was no response from the vessel.

The Raglan Coastguard was sent to the area and the Auckland-based air patrol was placed on standby.

"We called on all stations for assistance to see if they could find a vessel or anyone around that area."

Caddy said a vessel close to the bar sighted a man in the water and pulled him out.

"The person plucked out of the water said two people had swum ashore, and directed the vessel to those people."

Rescuers saw one man on a rock and brought him to safety.

All four men were wearing lifejackets.

Caddy said the dramatic rescue showed the need for boaties to take safety precautions.

"It just shows the absolute importance of logging a bar crossing and wearing lifejackets at heightened times of risk," she said.

"It certainly gave the best chance of a positive outcome in today's capsize."