A milk tanker driver was rescued from the wreck of his mangled cab yesterday after he lost control and flipped in a devastating crash on a quiet country road.

The driver, understood to be Morrinsville man Robert Black, 45, was taken to Waikato Hospital with extensive leg injuries and possible back injuries after the smash on Roto O Rangi Rd just after noon.

Last night he was in a serious but stable condition at Waikato Hospital where he was expected to undergo surgery.

An investigation is under way to find out how the accident happened.

Although the wrecked tanker was labelled with Open Country Dairy logos, Mr Black collected his pay from Waharoa Transport which is contracted to the dairy company.

The experienced driver had been with Waharoa Transport for two years - working shifts of three days and three nights followed by three days off - before he clocked in at 6.30am yesterday.

The morning run delivering milk to Open Country's Waharoa Plant came and went.

But things took a horrifying turn on a sharp, damp bend at about 12.20pm.

Waikato Highway Patrol sergeant Marc Hepworth said Mr Black was heading north when, for some unknown reason, the milk laden trailer veered onto the verge.

"He has tried to correct it and he's been unable to correct it and he's lost control of the truck."

The truck and trailer unit spun out of control, flipped into a roadside paddock and snapped a power pole that brought down the live lines.

Mr Black was left trapped in what remained of the cab.

Emergency services arrived and firefighters forced entry and managed to pull him free.

Mr Black was conscious throughout.

The road was closed and power was cut for several hours as emergency services cleared the scene.

Mr Hepworth said the wreckage would be examined for mechanical failure as police attempt to ascertain whether it was Mr Black, the vehicle or the wet road conditions that caused the accident.

Mr Hepworth speculated that the driver could have been travelling that route every day and queried whether complacency may have set in.

Add a bit of wind, rain and a wet road and everything changes, he said.

"That's why we say drive to the conditions.

"It's the most important message that road police can get across. If the weather turns, slow down. If it's windy, slow down. The slower you're going the more time you have to react.

"He's lucky to be alive - the cab was totally squashed."

Sentiments shared by Waharoa Transport director Mark Clothier who, like Mr Hepworth, was last night thankful his employee was alive.

"You can fix a truck but you can't fix a life can you? We just hope he's alright."

Mr Black is one of about 100 drivers employed by the company that owns a fleet of 65 trucks.

Mr Clothier said they would look at supporting Mr Black's family. He is understood to be single but had a "couple of kids".

Their driving trainer would investigate the crash after police had ascertained what happened, he said.

Was driver fatigue a concern?

"Some people are different, aren't they," he said.

"What they do outside our work, we try and monitor it, but you don't know do you? When they leave here they're their own person."

They conduct random drug testing on employees and he said they've had a "good run" with driver safety.

- © Fairfax NZ News