Two people have died in a helicopter crash north of Kaikōura.

Locals raced to the wreckage to help after watching in horror as the helicopter, with five people on board, crashed at a rivermouth.

Three people seriously injured in the crash have been flown to hospital

"Further details regarding the deceased and injured, including ages and genders, will not be released until all necessary family notifications have been carried out," police said in a statement.

The crash took place at the Kekerengu rivermouth at Clarence, a small town 30km north of Kaikōura, at 12.42pm

A man first on the scene of the crash says the helicopter was completely destroyed.

There were six people on board the chopper when it crashed at a rivermouth north of Kaikōura.

Kekerengu resident Ian Mehrtens thought it was landing, until it started going around and around.

The chopper crashed on to the beach and he headed to the scene and helped remove people from the wreckage.

"I didn't really count [how many] because it was just the stress of the moment to get people out," he told Newstalk ZB.

He stayed at the scene until emergency services arrived.

Around six or seven police cars arrived from all directions before five or six fire support crew and doctors arrived too.

"Everyone is there now. I couldn't do any more so I just came home," Ian Mehrtens said.

'We just watched it go round and round and round'

Coastal Lodge owner Lyn Mehrtens watched as the chopper plunged to the ground, spinning in circles as it descended.

"We just watched it go round and round and round," said Mehrtens.

"It's scary. You're just so helpless. You can't do anything."

Mehrtens said her husband raced over to the crash site, and others in the community were on tractors doing what they could to help those inside the wreckage.

Everyone who could was helping until emergency crews arrived.

The chopper appeared to have crashed near the front of The Store, which was a popular spot for heli-tourists to visit.

A spokeswoman for Kaikoura Helicopters Ltd said it was not one of their machines.

St John has sent three helicopters to the scene - one from Wellington, Nelson, and Christchurch.

A spokesman says an ambulance was on the way from Kaikōura, as well as an intensive care paramedic and a manager from Blenheim.

He says the crews are still making their way to the scene after they were called at 12.42pm.

The 60km journey from Kaikoura to Clarence, which is located at the mouth of the Kekerengu River, will take 48-minutes to drive along State Highway 1, according to
Google Maps.

The drive from Blenheim, meanwhile, will take 52-minutes to drive just shy of 68km.

Police confirmed the crash near the Kekerengu rivermouth, north of Kaikōura.

"Emergency services were alerted to the crash at 12.40pm and are currently en route to the scene," police said.

"At this early stage there is no confirmed information regarding the number of people who were on board the helicopter or any injuries sustained."