A man's detached hand was preserved in ice onboard the helicopter flying him to hospital after a serious attack in broad daylight near Whakatāne.

Liam Brettkelly, a pilot for the Trustpower TECT Rescue Helicopter, was called yesterday afternoon to fly a critical patient with a severed hand and a serious head injury from Whakatāne Hospital to Waikato Hospital.

The 27-year-old man had one of his hands severed and suffered serious head injuries after an assault on McKenzie St in Taneatua just before 2.30pm.

The incident happened near the forecourt of the town's Gull service station.

Brettkelly said the man's hand was packed in ice in a bowl while he lay intubated and unconscious for the short journey between hospitals.

The hospital had already stabilised the patient, so the transfer was "quite straightforward", but something of this nature was always "challenging" for medical teams, he said.

"It really was a team effort."

Tāneatua is about 13km from Whakatāne in the Bay of Plenty. Photo / Supplied

The helicopter was equipped with ventilators and other medical items to ensure the patient's breathing remained stable, he said.

Rescue helicopter crews have seen a large number of severe injuries, so a single amputee situation was "not unusual", he said.

Brettkelly said he had heard that the man was taken to Whakatāne Hospital by a car, which actually passed the ambulance on the way to the scene.

A St John spokeswoman said they had sent one ambulance and a helicopter to the scene and one person was taken to Waikato Hospital in a critical condition.

Waikato Hospital had dealt with similar incidents before.

In 2009, a King Country meatworker saw his hand flapping around after nearly cutting it off with a bandsaw.

Yesterday's assault was being investigated by police.

Details including whether the victim was known to his attacker, the circumstances surrounding the incident or the weapon used were not available, as inquiries were ongoing, a police spokeswoman said.

There did not appear to be any risk to members of the public, she said.

Police were appealing for witnesses to the assault or for anyone who saw a black Great Wall ute in the Taneatua or Ruatoki area on Sunday afternoon to contact them.