The Civil Aviation Authority is investigating after a rescue helicopter crashed in Waikato on Tuesday evening.

The Hamilton-based Westpac helicopter was on its way to rescue two trampers on the Wharauroa Track in Mount Pirongia Forest Park, but ran into trouble shortly after 4pm.

Maritime New Zealand, who manage Rescue Coordination Centre NZ, says the heavy landing happened on Mount Pirongia, about 15 kilometres west of Te Awamutu.

Two additional helicopters were sent to recover the trampers and the three-person crew.

No injuries were reported.

Philips Search and Rescue Trust says the pilot, a critical care flight paramedic, and crewman were all extracted from the helicopter.

The crew were taken to Waikato Hospital as a precaution.

The three people were in their 40s, 60s and 70s.

The trust's spokesperson Sharni Weir says their focus is on supporting the affected crew and their families.

The CAA says it worked with police to ensure that the helicopter was secure overnight.

It says its investigators will continue working with the police and the operator to find out what caused the incident.

CAA has reported the incident to the Transport Accident Investigation Commission.

- RNZ.