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Police have named a lawyer killed when the van he was travelling in crashed off State Highway 1 south of Oamaru on Saturday.

Roger Alexander Fraser, 51, from Christchurch, was a front seat passenger in a van carrying six businessmen when it crashed off the road and into a tree at about 12.15pm.

Constable Darrin Low said the crash was still being investigated but it appeared the van lost control before going over a small embankment at Katiki, about 15km north of Palmerston.

"It glanced off a couple of cabbage trees and then struck another large one head on."

He said Mr Fraser died and the other five passengers were all injured, including one who remained in Dunedin Hospital with several broken bones.

The crash was one of four weekend road fatalities.

A fifth crash on the Wellington motorway at about 6.40am today killed one person and caused big delays for commuters heading into the city.

Inspector James Taare said the driver of a vehicle that crashed into a median barrier died and a second car crashed into the back of that vehicle on the southbound motorway a few hundred metres before Aotea Quay.

Another person was killed overnight in a crash northwest of Christchurch at an intersection on State Highway 77 at Coalgate near Darfield.

A Lower Hutt man's drinking was believed to be a factor in a crash which left him dead on Saturday morning.

Brodie Jackson, 41, was thrown on to the road after his car apparently hit the median barrier and was then hit side-on by a van.

The accident happened on the Western Hutt Road, just south of the Melling intersection at Lower Hutt, about 7.45am.

Senior Sergeant Jason McCarthy said it was believed Mr Jackson had been drinking before the accident.

"It is believed the deceased had been consuming alcohol in Wellington ... and this appears to be a factor," he said.

Police have also not yet named a 46-year-old woman killed after a head-on collision between her car and another vehicle at Whitford, south of Auckland, on Friday night.

Another person injured in the crash was taken to hospital and remains in a serious condition.