UPDATED 8.05pm: The body of a man killed in an explosion in south Auckland is still lying at the scene of the accident.

Police and WorkSafe New Zealand are investigating after the incident at Salters Cartage.

The man was one of two contractors carrying out work at Salters Cartage in Wiri.

Newstalk ZB's Gia Garrick is at the scene and said police are planning on keeping the scene in lockdown overnight.

Police won't say whether people will be back at work tomorrow.

Emergency services were called to Salters Cartage in Wiri just after 1.30 today after reports of a large explosion.

Managing director Ron Salter said the man who died was a contractor and was killed when a tank exploded.

He said two contractors were on site, measuring some walkways.

"We had two contractors on site that were here to measure some walkways, unfortunately one of them has decided to do some welding without permission and the tank has exploded."

He said the blast blew out all of the windows at Salters Cartage.

Four people have been treated for minor injuries.

Jim has a business two doors down from Salters and said the explosion blew out windows.

"We're probably 50 metres away and its blown all the windows out of one side of our building."

A St John spokesman said two road units along with two hazmat-trained personnel are at the scene.

The explosion was so big it was heard in Botany, Manurewa and Flat Bush.

And the Fire Service said one of the people who called 111 reported pictures being blown off their wall.

The NZTA said Roscommon Road has now reopened.

But Langley Road, Mayo Road and Bolderwood Place remain closed to traffic.

Drivers are being asked to follow the directions of Emergency Services who are at the scene.

Witnesses recall explosions 

Loretta lives in Howick and heard the explosion there, she thought it was something on her roof.

"I thought there was something on my roof - I ran upstairs to check. It was quite something here."

This witness Derek is a cab driver and says it sounded like a rock landed on his van.

"I looked at my van to see if it was alright, and then all of the teachers came running out from the blind school saying 'hey did you hear that?' and not long after that, there were streams of emergency services heading down Browns Road."

Jerry was right next to the explosion in an oil storage depot.

He told Danny Watson it was a huge explosion.

"Bits of metal probably flying 150 metres into the air...it's pretty crazy."