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.

"We are immensely grateful that our crew members onboard are safe and well," trust chief operating officer Chris Moody says in a statement.

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

The CAA says it worked with police to ensure that the helicopter was secure overnight and it remained under a police cordon, Moody says .

"The recovery process of the helicopter will commence over the next few days and will be determined by the Civil Aviation Authority (CAA), as the helicopter is situated in deep, dense bush," the trust says.

"We urge everyone to cooperate with the authorities and to refrain from entering the designated area until the recovery process is completed. The safety of everyone is our top priority, and we appreciate cooperation and understanding with this."

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.

"Despite this incident involving the Waikato Westpac Rescue Helicopter, we have three branded Westpac rescue helicopters in our Waikato fleet, one of which was involved in the incident, BK117-HHJ, we would like to assure the public that we are operational 24/7 and continue to be there for those who need us today," Moody says.

"We recognise that there are concerns about the nature and cause of the incident and we would like to remind everyone that this is an investigation that is carried out by the CAA and no one is at liberty to discuss any further details."

- RNZ.