"The wave was approximately one metre. It sucks out and comes in. It takes a couple of minutes. They are very long waves," Jeroen Jongejans, who runs Dive Tutukaka, told NZPA from his boat near the harbour entrance.
He said the water was discoloured indicating the energy level of the wave was very deep and had picked up debris from the harbour floor.
One of the marine markers indicating the course boats should take to get into the harbour was "violently shaking." He said the tidal flow was estimated to be about 12 knots which was very strong.
"It is very unusual for a body of water to move at that kind of speed." Mr Jongejans said he was in no danger but was in constant touch with civil defence authorities and was keeping a constant lookout for surges.
Kate Malcolm, also from Dive Tutukaka, said there had been several strong surges in the marina there had been a rise and fall in the water level of about a metre and a half. "It has resulted in a washing machine action in the marina.
"The piles are moving around a lot when the surges come through. There is about 12 knots of current at the entrance when it comes through and the lines are quite tight on the vessels in the marina."
She said normally the tidal flow was hardly noticeable in normal conditions and the 12 knot current was very unusual and very strong.
No damage had been reported.
"But some of the boats certainly looking like they were getting tossed around," she said.
The flow arrived as Northlanders were repeatedly warned to stay away from beaches and not try to watch events.
Northland Civil Defence spokesman Matt Johnson said the highest surges of the first wave he had been told of were about 20 to 30cm, but he said higher waves could be on their way.
"We are still having issues with sightseers," Mr Johnson said after the first waves arrived about 9.45am.
"We are reminding people that the first waves are not necessarily the biggest. There are no evacuations, but we're advising people to stay away from the beaches. They don't need to be there."
Mr Johnson said surges had been seen at Tutukaka, which also experienced them during a previous tsunami alert, and Waitangi.
There had also been some discolouration of the water noted.
