Gases from a P lab in a cave on the Coromandel Peninsula are believed to have been responsible for killing two men cooking the drug.
The bodies of the men were recovered from an old mine shaft on the 309 Rd between Whitianga and Thames yesterday.
Police said they had taken "material" from the cave to be analysed but would not comment on whether there was a P lab or an explosion.
Police have also not revealed who alerted them to the bodies on Saturday afternoon.
Firefighters were on alert for chemicals or flammable liquids when they were called to the scene about 9.30pm on Saturday.
It took most of yesterday to recover the bodies from the old mine shaft, which is hidden beyond the road in dense bushland.
Detectives from Waikato are investigating the fatalities and yesterday had not revealed a cause of death.
A post-mortem examination is scheduled to take place in Auckland today.
Neighbours said they had been told the men were killed by the explosion of a P lab.
At least one of the deceased men was known to some locals but those who knew him declined to comment on his death.
Police said the names of the men would not be released until their families had been informed.
While most meth labs are found in houses, garages or sheds in residential areas, police have uncovered some in less obvious places, including caravans, shipping and storage containers, motels and baches. A lab was also found in a car boot.
