Two people have died and five others are badly injured after a serious crash on the Coastal Highway, also known as State Highway 60, in Redwood Valley.

Police were called to the crash site, about 25 kilometres west of Nelson, at 10.48am.

A car towing a caravan collided with a truck carrying scaffolding. A third vehicle was also thought to be involved.

Police first said some of the occupants of the vehicles had critical injuries, but confirmed this afternoon that two people had died.

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The road is closed and emergency services and the Serious Crash Unit will remain at the scene until late this afternoon, police said.

Three ambulances, two response units and a helicopter were sent to the crash site, where Maisey Rd and Westdale Rd meet the highway.

Paramedics had rushed five injured people to Nelson Hospital's emergency department, St John spokesman Ian Henderson said.

Two people with serious injuries were taken there by Nelson Marlborough Rescue Helicopter, and two more who were also seriously hurt were taken by ambulance, as well as a fifth person with moderate to serious injuries.

Emergency personnel transporting a person injured in the crash to the Nelson Marlborough Rescue Helicopter. Photo / Jessie Johnston, Nelson Weekly
Emergency personnel transporting a person injured in the crash to the Nelson Marlborough Rescue Helicopter. Photo / Jessie Johnston, Nelson Weekly

Henderson was unable to confirm whether anyone had died at the scene.

Firefighters used the jaws of life to free three people who were trapped in the wreckage, a Fire Service spokesman said.

A local resident said she heard the "huge" bang the collision made from her home and jumped in car and rushed to the scene.

Scaffolding was all over the road when she arrived and she helped clear the road and comfort the family who were travelling behind the vehicles that crashed, the woman said.

She told the Herald the crash had happened at the Westdale Rd intersection with the highway, which was on a blind corner.

Another woman who drove past the scene said it was "carnage".

Another nearby resident posted on social media that the collision made the "most horrendous noise" she'd ever heard and sent her leaping for her phone right away to dial 111, even though she couldn't see the crash.

Traffic is being diverted at Gardner Valley and SH60, police said.

The highway is closed near the intersection with Maisey Rd, an NZ Transport Agency spokesman said.

Light traffic bound for Motueka and Richmond is being detoured down Moutere Highway at Maisey Rd.

All heavy traffic is being detoured via the Moutere Highway.

Police asked road users to avoid the area if possible, or take diversions where directed.

Today's isn't the first serious crash at the intersection.

An elderly woman, Hazel Margaret Gill, died in Nelson Hospital days after the car she was a passenger in collided with two other vehicles at the intersection in December 2015.

After Gill's death local residents started lobbying NZTA to add right-turning lanes for vehicles turning into Westdale and Maisey roads from SH60 before someone else was killed or seriously injured there.‚Äč