Key Points:

Up to 80 firefighters are battling a large blaze at an abandoned cool store building in Auckland.

The fire, at the Southdown Freezing Works building on Hugo Johnston Drive in Penrose, began just before 6pm.

The three storey building was engulfed in flames and the firefighters and support crew were working to control the fire from outside as it was not safe to enter the building, northern fire communications shift manager Mau Barbara told NZPA.

It was reported nearby factories were being threatened by the blaze.

Eyewitness Brendan Myers of Pakuranga says the northern end of the coolstore was still ablaze past 10pm while the southern end seemed to have burned out.

Mr Myers said there had been "a few large explosions" heard coming from within the building. He also said a nearby computer recycling centre and car parts dealership were under threat as the fire continued to spread almost 200 metres from the point where it is thought to have started.

Fire service assistant regional manager Peter Wilding said the building was a "large complex comprising many old buildings".

The fire was gradually spreading along the complex, he said.

The old structure was unsound and firefighters were "firing water into the building" and using aerial trucks with ladders to get higher.

An aerial truck arrived from Hamilton to help and other engines had been "shuffled around" to provide cover throughout Auckland.

Police said the area was blocked off from the intersections of Great South Rd and Vestey Drive and Great South Rd and Sylvia Park Rd.

They asked the public to stay away from the area.

Nearby commuter train services were suspended due to the incident.

No one was believed to be injured.