The construction site company where five people were badly burned in an explosion this morning say they are a tight team and its immediate focus is on the injured workers, their whānau and those they worked alongside.

The blast knocked some people out of their shoes and shredded clothing remained at the scene.

Hawkins spokesperson Helene Toury confirmed the incident happened at the company's construction site in Wynyard Quarter.

"Our immediate focus is to support the injured workers, their whānau and the team on site. We are working with the relevant authorities to establish exactly what occurred."

She said the company was grateful for the efforts of the first responders - Fire and Emergency New Zealand, the New Zealand Police and St John New Zealand.

"We are a tight team and our thoughts are with the injured workers and their whānau."

She said the company would not be able to comment on today's events until the incident investigation is completed."

Shredded items of clothing where injured workers were treated on the Halsey St footpath. Photo / Michael Craig

A gas cooker left on overnight is suspected of causing an explosion that left five injured - four seriously hurt - at a downtown wharf building site.

• 'It's so crazy' - five injured in explosion at Auckland wharf
• Explosion injures man at Auckland property

The incident triggered a large-scale response from emergency services who raced to the Halsey St site around 6.30am.

WorkSafe has been notified and has opened an investigation.

A spokesperson said as it was currently making enquiries as part of the investigation it couldn't comment further.

Five injured in the blast were taken to Auckland hospitals for treatment. Photo / Michael Craig

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

Eyewitnesses reported seeing firefighters douse the victims with hoses as they awaited ambulances.

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

A large scale emergency response in Halsey St just after 6.30am. Photo / Michael Craig

Auckland Central Station senior station officer Frank Walsh told Stuff firefighters were the first to arrive at the scene.

"On arrival, we were confronted with five quite badly burnt patients down by the side of what appeared to be a shipping container.

"We arrived before the ambulances, so had to triage the patients and administer first aid, including beginning to cool the burns."

The Halsey St construction site at the scene of the early morning blast. Photo / Michael Craig

He said firefighters directed the water on the burns with fire hoses.

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.

Work had not started at the Hawkins construction site on Pakenham St West when the explosion occurred. Workers were sent home and the site was closed today with the site posing no further risk to the public.