Six lifeguards are motoring' />

A "scary" accident this morning disrupted surf lifeguards' historic journey on small rescue boats around New Zealand.

Six lifeguards are motoring 5200km in two inflatable boats powered by 30 horsepower Mercury outboard motors to commemorate 100 years of surf lifesaving in New Zealand.

Click here to follow their progress on a live map.

The 40-day estimated trip was delayed after one of the boats flipped over about 11.30am.

Lifeguard Jason Harvey told NZPA he and three others stopped at Birdings Flat, 45km south of Christchurch, for lunch and fuel.

"We spent about half an hour on the beach, and while we were there the swell picked up a little bit, and so the tide came in," he said.

"As we were launching, the first wave came in, pretty much picked us up and threw us over our heads. We went pretty high."

Mr Harvey said it was a bit scary, but the group was close enough to shore.

"I haven't been in a boat that has flipped many times, but it's alright because you've got all your gear on."

The engine was damaged, but crew members fixed it on site, he said.

Three hours later, the group went to a safer place to launch and headed to New Brighton for the night.

They will have a meeting at 4.30am tomorrow to assess the weather, and likely head out to Kaikoura.

The team, who are six days ahead of schedule, left Auckland on January 5 and headed north to round Cape Reinga before heading down the west coast of the North Island, across Cook Strait and to the Milford Sounds.

They were stuck in Breaksea Sound because of the bad weather for two days before they headed to Preservation Inlet on Friday.

The trip would also create history by being the first to circumnavigate the country in an inflatable craft under four metres long.

Though historic, the trip could be slightly boring with no entertainment on board.

"A couple of boys sing to themselves," Mr Harvey said.

"You can't talk to each other ... because you are wearing a helmet and the engine is really loud. You just kind of focus on the waves in front of you and just pass the time as best possible."