Two children have been orphaned after a family helicopter trip went tragically wrong on New Zealand’s South Island on Tuesday.

Two adults – named by local media as pilot Andrew Davidson and his wife Lin – were killed when their helicopter crashed in Clarence, about 200 kilometres north of Christchurch.

Joining the pair on their joyride were their own two children and a third child.

The three youngsters, believed to be aged between about seven and 13, were seriously injured. They were flown to Christchurch Hospital for treatment.

“It’s come as such a shock. The children have been left without parents,” a relative told news outlet Stuff.

The horror scene was witnessed by Lyn and Ian Mehrtens from their bed and breakfast near the mouth of the Kekerengu River.

Mr Mehrtens said the pilot was in control of the descent until the last 30 or 40 metres, when the Airbus Helicopter EC120 spiralled to the ground and crashed into the lapping waters of the beach at low tide.

“It started spinning … then it just disappeared … clunk … bang. I thought ‘s–t, oh my god’,” he told the New Zealand Herald.

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A small group of locals, including Mr Mehrtens, arrived at the scene well before emergency services.

They dragged the passengers and deceased pilot out of the helicopter and then used a tractor to winch the downed aircraft from the sea.

“I carried the wee girl up the beach to where her mum was lying. She was asking me ‘where’s my mummy … is my mummy all right?’,” he said.

“I said ‘yeah, she’s all right’ but she was far from it.

“[The children] were screaming in pain … the older girl, she wasn’t good.

“There were six of us trying to get them out. The worst part was trying to get them out of their seatbelts.”

Mr Mehrtens said one of the girls was aged about eight and the other was in her teens. The third child was a boy of about 10.

On Tuesday afternoon, NZ Police said the three children had been seriously injured. They have

The Transport Accident Investigation Commission has opened a probe into the deadly crash.

On Wednesday morning, police advised of a second helicopter crash in as many days, on at a rural property on the Mahia Peninsula on the east coast of North Island.

St John advised the pilot, who was the only person aboard, was “moderately injured”.

-with AAP