At least two helicopters - believed to be military-grade Sikorsky choppers - swooped low over Auckland last night, shaking residents' homes before they landed at the Domain and were greeted by an ambulance.
The choppers were part of a military training exercise but many residents were left bewildered and surprised by the force of their power.
Remuera resident Adele Print emailed the Herald to say the two helicopters swooped over her house. "Incredibly loud, the house shook, sounded like they were landing in our garden. One of our children saw them fly past the garden."
A Newmarket resident said: "It was like something out of MASH - like a war zone. Our entire apartment block shook."
Residents from other central and eastern suburbs also reported the helicopters flying low.
One of the choppers landed on a main sports field at the Auckland Domain - near the historic wooden grandstand - and was greeted by a St John ambulance with flashing lights. The second helicopter hovered as this was happening.
A witness said an ambulance gurney was taken to and from the helicopter - but it appeared there was nobody - or thing - on it.
A statement from the Defence Force (NZDF) confirmed the helicopters were part of a training exercise involving members of the United States military.
"The NZDF and a United States Army Aviation Regiment will conduct joint exercise in Auckland and Waiouru from 8 to 23 May," the statement said.
"The exercise will involve a large number of military personnel, including special forces from both countries, as well as aircraft.
"Its purpose is to practise counter-terrorism integration techniques between the two countries."
The exercises would run day and night and involve aircraft and live firing within the Kaipara Air Weapons Range.
As well as central Auckland, elements of the training will be carried out in Whenuapai, Kaipara, Papakura and Waiouru.
Herald readers believe the helicopter pictured is a Sikorsky UH-60 Black Hawk, a model used throughout the United States military.
The NZDF said the New Zealand and United States armies have trained together several times in the past.
"The exercise has been planned since 2018 and is not in response to the recent events in Christchurch.
"Members of the public may see personnel conducting military activities from helicopters in exercise areas.
"There is no need for the public to be concerned if they see military action in Auckland over this period."
A woman who saw the helicopters in the Auckland Domain said one landed on the main cricket field, near the historic wooden grandstand.
She said a gurney was taken to and from the helicopter but it did not appear anyone - or anything - was on it.
Meanwhile, the second helicopter swooped around the Domain.
"It was so low on its first cross that our house shook," said one resident.
Another bewildered resident said he saw the helicopters land on the Domain about 8pm before they took off around 10 to 15 minutes later.
A spokesman for Auckland Westpac Rescue Helicopter said it was not involved.
A spokeswoman for St John said they also were not involved and a police spokeswoman said she was unaware of any incidents involving helicopters and the Domain.