A chemical explosion from a suspected P lab in one of Auckland's poshest streets seriously injured two men and scuttled dinner and theatre plans for some of the eastern suburbs' wealthiest residents.

Police cordoned off a section of Paritai Drive in Orakei while hazardous material specialists were brought in after reports of the explosion at 6.45pm yesterday.

One of the victims was in a critical condition and the other man was in serious condition in Middlemore Hospital's serious burns unit last night.

Three other adults and a child, aged about 3, were in the house.

All were hosed down by the Fire Service.

About a dozen residents milled around outside while fire engines and marked and unmarked police cars clogged the street, where palatial properties sit alongside cheaper, older housing.

One man walked around, wineglass in hand, and neighbours jokingly asked one another, "What does the P stand for in Paritai?"

One asked the Herald to report that the explosion happened at the cheap end of the street.

Police say the explosion took place in a garage at the rear of the property at 144 Paritai Drive.

A neighbour a few houses away was home.

"There was a bang, and then I heard the helicopter - it was just going round and round and round."

The Fire Service and police arrived, including a plainclothes officer who "pulled his gun out of his back pocket and said, 'I think you should go inside'."

Another resident reported someone was taken away from the address in handcuffs early one morning a couple of months ago.

Senior Sergeant Danny Meade said a flash explosion - where heat source and a combustible material had come together - had occurred in the garage where the two men were.

He said staff of the Institute of Environmental Science and Research were assessing their find.

A P lab was "always a suspicion" but would only be confirmed later.

Mr Meade said the uninjured occupants were detained under the Hazardous Substances and Dangerous Organisms Act.