Three people are believed to have died and eight people were injured after a multi-vehicle crash on State Highway 1 between Bombay and Ramarama.

All lanes have been forced to close and closures are likely to be in place into the evening as emergency services clear the scene. Motorists are being urged to delay their travel if possible.

A truck, a van and at least two cars are thought to be involved.

Tamati Cassin, a motorist who arrived at the scene soon after it happened, said he saw three bodies in the van, as well as two people injured in a separate vehicle.

He said several members of the public ran to the aid of those involved.

”When it happened, everyone just jumped out of the cars and ran over to the van and the truck, because the truck was pretty badly damaged, and the van with the bodies in there, people just didn’t know what to do, and [they were] just trying to get them out.”

It appears a truck has veered through the wire median barrier and into oncoming traffic on State Highway 1 between Bombay and Ramarama. Image / Supplied

He said it appeared the truck had been travelling southbound when it blew a tyre and crossed the road, where it went through the barrier wires, and collided with a van.

”It’s all bad down here. Everyone’s banded together. The ambulance has got to all the injured. They’ve just covered up the van, and I think they’re going to get everyone moving.”

Images from the crash show the wire median barrier wrapped around the front wheels of the truck.

Wreckage from the truck and vehicles it has collided with could be seen strewn across the motorway.

Dazed motorists were sitting on grass verges while others walk around. Bystanders tended to the injured near their wrecked vehicles.

A passerby who stopped at the scene could be seen using power tools from his vehicle to help extricate people trapped in the vehicles involved in the crash.

Police confirmed the South Auckland crash was reported to them about 1.47pm today.

Early indications suggested multiple people have received critical injuries, police said.

St John Ambulance said it was treating eight patients, including one in a critical condition, three moderate and four minor. Six were transported to various destinations.

St John said it was sending 10 vehicles to the accident. A helicopter was also flying to the crash scene.

It said four ambulances, two rapid response vehicles, two operations managers, and one Westpac road unit have responded.

Traffic backed up at Bombay after a fatal crash.

Posts to social media show a truck, van and at least two other cars with major damage and people walking over the motorway.

According to Google Maps, traffic is backed up for nearly 5kms.

The motorway has been closed in both directions and diversions are in place.

The New Zealand Transport Agency said detours for southbound motorists are the Ararimu Rd off-ramp.

Northbound motorists should detour via Bombay at Great South Road.

The Serious Crash Unit has been advised.

The Northbound carriageway has been fully blocked between Bombay and Ramarama.

NZ Transport Agency also confirmed all northbound lanes on State Highway 1 between Bombay and Ramarama are currently closed due to a significant crash.

“The right southbound lane is also blocked and people are asked to pass with extra care and expect delays. A full southbound closure may also be necessary so motorists are asked to follow directions of response crews at the scene,” NZ Transport Agency said.

“NZ Transport Agency Waka Kotahi recommends that people delay their travel if possible, avoid the area and use another route.”