It could take up to 17 months before investigators know why a helicopter crashed and caught fire in Rotorua last week.
An investigation is under way into a Guimbal Cabri G2 helicopter crash landing on Hawthornden Drive in Tikitere on Friday afternoon.
A resident has described watching the low-flying helicopter's cockpit fill with smoke, before the pilot landed heavily in a paddock near his home. The pilot then sprinted from the helicopter, shortly before it burst into flames.
The Civil Aviation Authority Safety Investigation Unit gathered information about the crash over the weekend.
Civil Aviation Authority spokesman Mike Richards said the investigation had been handed over to the Transport Accident Investigation Committee (TAIC). He said his team was still working with TAIC in the background, but TAIC was taking the lead.
TAIC spokesman Roger Foley said it had opened an inquiry and two investigators had been at the scene throughout the weekend.
He said they had packed up parts of the wreckage that were being sent to Wellington.
"Normally it can take a year to 17 months for this kind of investigation. Our job is to find out the causes and circumstances that lead to these things. We need to be really thorough, there will be cross-checking with the builders of the aircraft as well.
"The reason we do these investigations is to find out what went wrong and to use that information so we can try to prevent it happening again," he said.
He said they may take more parts of the wreckage if needed.
Rotorua fire brigade assistant area commander Hamish Smith said the site cleanup had been handed over to the Rotorua Lakes Council because it was a hazardous site.
The council's transport and waste solutions director, Stavros Michael, said the council operated the only site in the district for the storage and/or disposal of hazardous materials - which was at the landfill.
"Potential hazardous materials at this site could be fuel, byproducts of engine parts or byproducts of other parts of the helicopter, such as those made with plastics. We won't know what, if any, hazardous materials there are until an assessment has been done."