Stratford police today named two pilots who died when an Auckland to Blenheim plane carrying items sent by courier, crashed in Taranaki about 10.15pm last night.

They were Clive Rodger Adamson, 43, of Wellington, and Anthony Brian Arthur Drummond, 41, of Manukau City.

Inspector Frank Grant said the bodies of the two men had been recovered from the crash scene and were being taking to New Plymouth where a post mortem would be carried out.

Among the pieces of wreckage was the cockpit area found about 12.30am, containing the bodies of the two pilots.

About 15 to 20 people had come into the police station today with items of debris and witness accounts, he said. Reports varyied from "a ball of fire in the sky", to "a ball of fire on the ground".

The debris had been found up to 15km from the farmland -- about 5km east of Stratford -- where the fuselage and cockpit had been found.

Major pieces of wreckage had been found in gullies and wooded areas, with the Fire Service being called in to put out fires.

It appeared the aircraft turned off course and went off radar before the crash, Mr Grant said.

The Transport Accident Investigation Commission said it had sent two people to Taranaki today to investigate the cause of the crash.

The plane was a Fairchild metroliner SA227-AC, registration ZK-POA, chief investigator of accidents John Mockett said in a statement.

A Blenheim air cargo pilot who has been in the business for many years said investigators would look first at whether someone had posted "undeclared hazardous goods" that should not have been sent.

"Aeroplanes don't come down like this," he said. "It is not normally this dramatic. It is going to be something unusual."

Such goods could include anything combustible -- turpentine, for example.

The pilot said there had not been a mid-air collision and there would not have been birds up there.

After cargo, the next possibility was mechanical, he said.

The incident was an unfortunate tragedy that involved two very experienced pilots.

New Zealand Post spokesman Ian Long said there was nothing to suggest any hazardous substances were on board.

"It wouldn't help at all to get into speculation at his stage," he said.

He said people had a responsibility to declare hazardous substances and there were checks and balances to ensure unsafe material was not sent.

The plane had been carrying items sent through courier brands Courier Post and Skyroad, largely all destined for Blenheim and Nelson.

The brands were operated by the company Express Couriers, a joint venture between NZ Post and DHL.

The aircraft had been operated by company Airworks on behalf of NZ Post.

A resident Geoff Hunger told NZPA the plane had shaken his house, making a noise something like a fighter jet, as it went overhead.

He thought the noise had been so intense inside the house probably because the plane had been so low at the time.

"We wondered what was coming through the house as it went over the top of here. That made us look out the window and you could see the thing on fire," he said.

"It was just a ball of flames ... It was like you'd got a big bonfire in your backyard as it went through."

After hearing the noise and going outside he had seen "this orange glow going through the sky and about 20 seconds later there was just a big explosion (in midair), I suppose, but you didn't hear it from here", Mr Hunger said.

"When it exploded you saw the big, big flash of exploding, then you saw what would be the burning bits of the plane falling out of the sky."

He had thought it might be a meteor, but "if it was a shooting star, she was one hell of a shooting star."

Another resident, Clair Edwards, said the noise had given her a fright.

"It was a huge, huge noise ... unbelievable."

At first it sounded something like the noise made when young motorists did "donuts" on the road, she said.

"But I thought, it's too heavy. Then it just got louder and louder and then this huge explosion then dead silence, totally dead silence."