Five people have been injured in an explosion at a downtown wharf in Auckland this morning.

The blast at the Hawkins construction site on Halsey Street is being blamed on a gas cooker but authorities have not confirmed the cause of the explosion.

Four of the injured have been left with serious injuries and have been taken to Middlemore Hospital and one suffered moderate injuries and was taken to Auckland City Hospital.

Shredded items of clothing can be seen on the road near the scene of the explosion.

Shredded items of clothing can be seen on the road near the scene of the explosion. Photo / Michael Craig

A man who had worked with those injured told Stuff the explosion happened inside a portacom at the site.

"One of the boys was cooking some leftover meat last night and I think the gas cooker must've accidentally been left on.

"This morning when people opened it up it exploded," the man told Stuff.

Work had not started at the Hawkins construction site on Pakenham St West when the explosion occurred. Workers have been sent home and the site will be closed today. There is no further risk to the public.

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The incident happened just before 6.30am.

The scene in Halsey St after five people were injured in an explosion. Photo / Michael Craig

A worker at the nearby Tuck Shop bakery and espresso told Newstalk ZB she didn't hear any explosion or any noises but did smell smoke coming through the doors.

Speaking about the construction site, she said: "They normally just get on with work and it's never really noisy or busy here, but this morning is hectic, with all the firefighters, it's so crazy."

A large number of ambulance, fire and police vehicles are lining Pakenham St West.

One person was seen wrapped in a blanket being spoken to by St John paramedics.

Another man with no shoes on could be seen limping down the street.

Emergency services at the scene of the Halsey St explosion which left nearly half a dozen injured. Photo / Michael Craig

The police spokesperson said police were assisting Fire and Emergency with an incident on Halsey St, Auckland CBD.

The incident was reported to police around 6.25am.