Key Points:

Two badly burnt men have been flown by rescue helicopter to Middlemore Hospital in Auckland apparently after an illegal methamphetamine lab blew up today.

The men were first treated at a medical centre in Wellsford, north of Auckland.

Fire Service shift manager Steve Smith said the two men had severe burns.

At this stage it is not known where the blast happened.

He said if they found where the men had come from they expected to decontaminate the building.

The Fire Services hazardous materials truck arrived at Wellsford about midday and Mr Smith said staff from the medical centre would be put through a water bath.

"We set up a tent and sprinklers and through you go - buck naked," he said.

The two injured men were to go through a special decontamination unit at Middlemore.