A search warrant has been executed at a Waikato landfill burning since August.
A two-dozen strong team led by Waikato Regional Council began a two-day examination of the dump at Pukemiro this morning.
"This search warrant is simply a regulatory agency working to establish the truth of what has happened here," council regional compliance manager Patrick Lynch said in a statement.
The search would feed into an investigation into whether the Resource Management Act had been breached by Puke Coal Limited, Lynch said.
This comes after accusations from local people that plastic waste had been dumped illegally that was fuelling the fire.
Resident Bill Rosoman said it was good to see some action.
He said he wrote to authorities on Monday asking if they had established if the fire was out, or if other fires might be burning because there was still a smell of sulphur.
A precautionary health notice was lifted in late November, after fire crews told an inter-agency response team that there was no evidence the fire was still burning.
Puke Coal has been approached for comment.