A kayaker who was attempting to cross the Tasman Sea to New Zealand has been forced to turn back after his satellite phone became waterlogged.

New Zealander Scott Donaldson says he had managed to kayak about 30 nautical miles after leaving Coffs Harbour on Wednesday, before pulling into Port Macquarie.

Mr Donaldson had been planning the trip for three years to raise awareness about the importance of exercise to help asthma.

"The dry bag that [the phone] was in wasn't dry anymore," he said. "It leaked and ruined the sat phone.

"[It was] a bit early on for those major problems to be happening."

Mr Donaldson is now trying to find up to $3,000 to replace the phone and hopes to resume his attempt next week.

He says having to turn back is frustrating, but both patience and planning are important.

"I was about to jump on a current that was going really fast and heading east and would have taken me a good 100 miles easy," Mr Donaldson said.

"But there is no point in making decisions that get you to the end in a dodgy state.

"You've got to do the best planning you can. So patience is a definitely a virtue that is required."