The Southwestern motorway has now been fully reopened, police said. All lanes were opened by 9.30pm.
A truck driver died in the crash on the Southwestern between the Dominion Road on-ramp and the Hillsborough Road off-ramp at about 4.20pm.
St John Ambulance duty centre manager Norm Ngatai said a recycling or rubbish truck had overturned on the motorway.
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The cab separated from the truck and "ended up on the opposite side" of the motorway.
A man in his thirties was believed to have been thrown from the cab.
The crash had left a significant amount of debris over north and south bound lanes, police said.
The Southwestern Motorway was closed to all traffic in both directions from Hillsborough Rd to Dominion Rd, and was expected to remain closed until 9pm.
Police warned motorists to expect significant traffic delays as the peak flow traffic period approached.
Motorists were urged to either delay travel or seek alternate routes.
Police said the delays would especially impact people travelling to Auckland Airport.
Traffic updates are available from the New Zealand Transport Agency website.
The police serious crash unit and commercial vehicle unit are investigating.
A 13-year-old girl has died in a crash on a notorious stretch of State Highway 1 north of Wellington.
Two vehicles collided on SH1 near Otaki early this afternoon. Police had established that three people were involved in the crash - a driver and passenger in a Subaru vehicle, and a driver in a Ford Falcon vehicle.
Rescue services at the scene of the crash.
The girl was a passenger in the Subaru. She was not believed to have been related to the driver.
"Preliminary indications suggest the Subaru was driving on a grass verge by the side of the road when it has pulled out directly into the path of the oncoming southbound Falcon vehicle," Senior Sergeant Sarn Paroli said.
Both male drivers were taken to Palmerston North Hospital in serious condition. The highway was expected to be closed this afternoon and traffic was being diverted.
Ronan Apiti said Buck the dog was like one of his children.