UPDATED 11.03AM: A large fire which burning since 4am this morning at a paintball park south of Auckland has been extinguished.

The blaze at Asylum Paintball in the former Kingseat Hospital broke ripped through a two storey, 60x60 metre vacant building, which was part of the old isolation ward.

Fire Service spokesperson Paul Radden said eight crews of 30 firefighters are monitoring the situation and dampening down hotspots.

A fire investigator is there and will start looking into the cause of the blaze as soon as it's safe to do so. It's not believed to be suspicious. 

Fire crews are expected to be there until about midday.

Alex Malikov, the owner of Asylum Paintball which operates out of the building, said it was being used as a playing arena with only furniture and discarded items in it.

He says firefighters have told him the structure will probably have to be pulled down.

"I'm quite upset at the moment," he said. "It all came in as a shock."

"It's a very cool, very unique building. It's part of Auckland's history that we had a lease of for three and a half years."