Two men out fishing leaped into the sea when their boat caught fire near the Pinnacles off Whangamata on Saturday.

One man is today in Waikato hospital being treated for serious burns, after being flown there yesterday. The other man was treated at the Whangamata Medical Centre.

The Whangamata boat caught fire about 1.30pm, and burned to the water line and sank. It was several kilometres from shore, but the smoke and flames were clearly visible from the beach, says Whangamata Coastguard president George Williams.

The men were rescued by another boat nearby and brought ashore.

It was not yet known what caused the blaze.