One of the world's rarest whales has been spotted heading north off the New South Wales south coast, in one of the first sightings of the whale season.

Migaloo, the male humpback, was photographed with a mobile phone camera off Green Cape in Eden on Tuesday morning.

The unique mammal was once thought to be the only all-white whale in the world and is often seen off Byron Bay during the last week of June.

The founder of the White Whale Research Centre, Oskar Peterson says it is not unusual to sight Migaloo, but it does take some luck.

"If you're lucky enough to get out and see him, then you are. It's just a matter of luck," he said.

"I know from Byron Bay to the Gold Coast, the last week of June to the first week of July is that two-week window where he'll go past.

"Now's the time down there in Eden, down the south coast and Illawarra to get out there over the next couple of weeks, you'll have a good chance of spotting him."

Mr Peterson says the rare whale is hard to miss when he does swim past.

"He sort of glows in the water like a fluorescent blue. He's quite an amazing sight," he said.

"He's been around for quite a while and he cruises up and down the east coast of Australia every year, but some years he goes missing in action so to speak."