A person has been arrested in what police are calling an "incident" that has left multiple people injured in Auckland's North Shore.

Emergency services were called to Murrays Bay on the North Shore, with locals saying police and ambulance vehicles began arriving about 11.30am.

Police said they were still working out how many people had been hurt, and the nature of the injuries. They said a person was in custody and assisting with inquiries.

St John Ambulance confirmed staff were helping but would not give any more information.

The entire beach was closed off, and police set up a cordon about 50m from the scene.

A police cordon after an incident at Murrays Bay on the North Shore on 23 June 2022.

Police at the scene in Murray's Bay. They said they were still working out how many people had been hurt. Photo: RNZ / Nick Monro

The nearby Montrose Cafe Bistro and Bar's manager Damien said he had spoken to people coming up from the beach, and rumours about what happened were spreading like wildfire in the typically quiet community.

"People came from the beach and had said that the offender had stabbed some people in Murrays Bay and then he ran over to Mairangi Bay where he was struck with a crutch from a man," Damien said.

"And then the police got him and he went away in an ambulance."

As he spoke to RNZ, he said he could see police cars entering and exiting the cordoned-off area.

A police cordon after an incident at Murrays Bay on the North Shore on 23 June 2022.

Photo: RNZ / Nick Monro

"Another undercover cop car just speed off down the road and then another marked police car is driving away from the scene," he said.

"There's a roadblock just outside our cafe. Just a police car parked horizontally across the road stopping traffic going in."

A woman working in a shop in on Auckland's North Shore said it was scary having so many police and ambulances converging on the area.

Shenee Birch works at Janbells Uniforms in Mairangi Bay and said she was told a man had been stabbing people at a nearby beach then fled towards Mairangi Bay on the walkway.

A knife on the ground after an incident at Murrays Bay on the North Shore on 23 June 2022.

Photo: RNZ / Nick Monro

"We saw heaps of police, ambulance and even maybe a fire truck heading to Mairangi Bay beach.

"From what I heard, apparently a man was fleeing because he had stabbed a few people at Murrays Bay.

"He then headed along the walkway that runs between the two beaches towards Mairangi Bay."

An RNZ reporter at the scene described the area as reasonably quiet with some nearby shops within the cordon. It was not possible to see what was happening on the beach, and only police vehicles were in view.

It is understood two schools in the area are not in lockdown because they are some distance from the beach.

People were asked to avoid the area.

More to come...

A crutch on the ground after an incident at Murrays Bay on the North Shore on 23 June 2022.