Peter Burling tells about the 'little mistake' that saw Te Aihe capsize in Auckland Harbour.

Star Team New Zealand helmsman Peter Burling has shrugged off the capsize of their new America's Cup boat as a "little mistake".

The mishap happened on Auckland's Waitemata Harbour on Thursday as the defenders continued their testing phase of their 75-foot monohull Te Aihe ahead of a Christmas break.

They were going through a foiling gybe - the most tricky manoeuvre - when they became unbalanced with their bow rearing up and their foils losing contact with the water.

EMIRATES TEAM NZ Te Aihe rolls over on its side during testing on Auckland's Waitemata Harbour.

Te Aihe lost speed and slowly rolled on to its side. They managed to get the boat upright and said all the crew were OK.

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"We had a really nice day on the Waitemata and were pushing the boat super hard around a few marks and we ended up making a little mistake out of a gybe and rolled it over in some pretty light breeze," Burling said later.

EMIRATES TEAM NZ Team New Zealand crew on their capsized AC75.

"But it's what these boats are designed to do and when you push the boundaries as hard as you can in practice, it's going to happen at some stage."

"We are just really happy they way we got it back upright and just carried on sailing for the rest of the day.

Earlier Team NZ described it as "a little whoopsie" and "part of the learning".

It is the first time one of the new foiling monohulls has gone over since the Cup syndicates launched the first editions in September.

The boats are designed to avoid going completely upside down when they capsize.

The incident happened in the shadow of North Head in about 10 knots of south-west breeze.

EMIRATES TEAM NZ Team New Zealand quickly got their boat up and foiling soon after the capsize.

The team used their chase boats to quickly right the boat.

A check for damage revealed no immediate issues and the crew resumed testing, getting the boat back up on its foils and powering off up the harbour.

"I can't say what happened on board but it looked like they had a bit of a high fly and then slowly rounded up in a high mode and a very slow capsize," Team New Zealand veteran Tony Rae said he he watched the action from one of the team's chase boats.

EMIRATES TEAM NZ Te Aihe revels in some heavy conditions during testing in Auckland.

"It was a good test of what you do to get it back up again. I think everything is all good, obviously it wasn't high speed so there were no issues and we can carry on."

It continues a watery trend for star helmsman Burling who twice went in the water while winning the recent 49er world championships in Auckland with Blair Tuke.

Emirates Team New Zealand have been pushing their testing phase, eager to get as much data off the new boat as their designers immerse themselves in the second generation boat that will be built and launched next year in preparation for the defence of the Auld Mug in March 2021.

EMIRATES TEAM NZ Team New Zealand goes down in a spectacular pitch-pole capsize during the America's Cup challenger semifinals in Bermuda in 2017.

They have had Te Aihe out in winds as strong as 24 knots without too many issues although they have had several heavy splashdowns off their foils without threatening to capsize until this mishap.

The quick recovery further validates the overall design of the new Cup class while Team New Zealand will be privately delighted their boat, built at their own facility, was robust enough to emerge unscathed from this accident.

The incident came after their British rivals INEOS Team UK warned about the consequences of crashing these highly technical boats.

The British syndicate and the New York Yacht club's American Magic both admitted they had capsize problems as they got to grips with their smaller-scales test boats.

Team New Zealand famously pitch-poled their foiling 50-foot catamaran in Bermuda on their way to winning the America's Cup in 2017.

That came in the challenger semifinals and they successfully undertook major overnight repairs to stay in the game.