Two women who were killed in a high-speed crash north of Auckland yesterday can now be named.

They were Eleshia McKinstry and Merle Jeschke, both 22, from Rodney District.

Today, police said the two cars involved in the crash hit each other at a combined speed of about 200kmh.

The accident left State Highway 1, near the Wellsford Golf Club, in a state of carnage with the two women dead and two other women with serious injuries.

Police said it appeared a southbound car lost control and crossed the centre line in appalling weather about 3pm to slam head on into a BMW.

Ms McKinstry and Ms Jeschke were the driver and the passenger from the southbound car.

A motorcyclist heading north had nowhere to go and was also hit by the southbound car, said Constable Caroline Ludford of the police serious crash unit.

She said at the speed the cars were travelling, it was "carnage", with wreckage from both cars and the motorcycle scattered over a wide stretch of road, which was closed for more than five hours.

The two seriously hurt women and a third person were taken by rescue helicopter to Auckland, while two with minor to moderate injuries were taken by road to North Shore Hospital.

The woman motorcyclist was moderately injured but may have more serious injuries which were still being investigated, she said.

One man who drove past the crash minutes after it happened said he was numbed by what he saw.

"There was a woman holding the motorcyclist in her lap because he was lying in the middle of the road, injured. He still had his helmet on.

"I don't know how anyone would have gotten out of the cars, I don't know how anyone could have survived it. It was a complete mess of metal."

The man said it was impossible to tell how the crash happened because the cars were so mangled. "I've seen a few accidents in my time, but I don't know how anyone got out of that. The cars were completely wrecked and were torn apart all over the road ... The two cars were sitting on the left-hand side of the road as you headed into Wellsford, but there was no way of telling if that's the way they were meant to be going," he said.

Senior Constable Barry Rose of Wellsford police said the people killed were travelling in the same car. He said the motorcyclist "got away reasonably lightly".

The owner of the nearby Castle Court Motel, Grant Kerrisk, said the stretch of road between Wellsford and Warkworth was notorious for crashes.

Accidents usually happened when it rained after a long dry spell, Mr Kerrisk said. The road was wet yesterday.

"It's a very treacherous stretch of road. Crashes happen there all the time."

The district's Auckland councillor, Penny Webster, said the stretch desperately needed to be improved. The blind corners, terrain and camber of the road were all risk factors.

"It's a very, very dangerous piece of road there and it desperately needs to be improved otherwise these fatal crashes will keep happening."

The proposed Puhoi-to-Wellsford highway extension would drastically lower the death toll in the area, she said.

In December 2007, the old Transit NZ cut the limit on the 10km stretch through Dome Valley from 100km/h to 80km/h.

From then until May last year, there were 23 crashes, including three deaths, compared with 36 crashes and seven deaths in the three years before.

Yesterday's collision happened at the edge of the farm of Greg Brown, who rushed to the end of his driveway.

"There was this huge boom. I heard it from inside my house ... which is 150 to 200 metres from the road. It was unmistakably a bad crash."

When Mr Brown got to the end of the driveway, he saw the mangled wreckage of the cars.

"It was pretty horrific. I've never seen anything like it in my life ... You couldn't tell what was what. There were bits everywhere. You could tell the motorbike, but the others were completely pulled apart."

With the highway closed, police diverted southbound traffic onto Centennial Park and northbound traffic onto Wayby Valley Rd, south of Wellsford.

State Highway 1 did not reopen until 8.30 last night.