Two fishermen are counting their blessings after escaping unharmed when their boat collided with a whale and sank off Evans Head in northern New South Wales.

Lismore men Michael Williams and Chris Churchill were heading out on a fishing trip at 5.30am on Sunday when they felt their 6-metre, half-cabin vessel hit something.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Listen Duration: 4 minutes 43 seconds 4 m 43 s Whale collision survivor Michael Williams talks about his experience ( ABC North Coast: Samantha Turnbull ) Download 2.2 MB

"It was still fairly dark at the time, and we were looking out the front of the boat and the next minute we felt this massive bang," Mr Williams said.

"We went into the air, got thrown around from one side to the other, and when I got up we were already ankle-deep in water."

Mr Churchill restarted the boat, but within seconds the men were standing in waist-deep water.

"Chris said 'Get out, get out', so we jumped out and by the time we were out the boat had sunk," Mr Williams said.

"It split the hull and opened it up like a nut.

"It filled it with water really quickly. Within 20 seconds it was under the ocean."

Mr Williams said neither he nor Mr Churchill saw the whale, but a fisherman on a nearby boat did.

"We didn't have a clue what it was. He [the fisherman] saw it breach the water as it hit us," he said.

"It would've had to have been big because it was like hitting a brick wall."

The men were pulled from the water by the fisherman, and saw seven humpback whales on the 5km trip back to land.

The boat collided with the whale about 5km off the coast of Evans Head. ( Supplied: Dee Hartin )

Whale may have felt threatened or protective

Organisation for the Rescue and Research of Cetaceans in Australia (ORRCA) president Ronny Ling said the whale may have felt threatened.

"They are very perceptive animals and they can judge the distances to boats really carefully and precisely," Mr Ling said.

"But they are wild animals, and they can be unpredictable, so we have to acknowledge that.

"This whale could have been avoiding predators, it may have perceived the boat to have been a threat — if it was a mother and calf, she's going to do everything she can to protect that calf."

Mr Ling urged skippers to keep their boats at least 300 metres from whales.

"This time of year there's a lot of mothers and calves and it's really important to give them that distance," he said.

Mr Williams said the experience had not put him off boating.

"We're actually looking at a new boat so we can go out and hopefully catch some fish this time," he said.

"But, yes, it's made me more wary of whales."