Four people flung from a vehicle that rolled multiple times on a Northland beach were lucky not to be crushed, police say.

Two people with serious injuries were flown to Whangārei Hospital by the Northland rescue helicopter after the crash 4km south of the Baylys Beach settlement.

The accident about 6.30pm on Tuesday also left the vehicle badly damaged.

Police believe alcohol and speed were contributing factors and charges are pending following results of a blood test on the driver. Volunteer firefighters from Dargaville helped St John staff and the helicopter crew with the injured patients.

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Senior Sergeant Ian Row said it was lucky those thrown from the vehicle were not crushed by the rolling vehicle.

"People not wearing seatbelts put themselves at massive risk and as well as breaking the law."

Row said beaches were dangerous to drive on.

"Beaches are roads so road rules apply but beach surface is different to roads. There are very soft patches which drivers don't realise and it doesn't take long for vehicles to roll," Row said.

"If you are driving impaired your ability to read the conditions is compromised."

Vehicles used on beaches also have to be roadworthy and drivers licensed.

In January this year, one person died and two were critically injured after a four-wheel-drive crashed on Ninety Mile Beach near the Waipapakauri Ramp.

In 2012 a Northland teenager died after falling from the back of a ute on Ripiro Beach.

She had been in a convoy of three vehicles travelling down the beach about 10am on December 20 and had been at an end-of-year function the previous night. She was travelling in the back of the ute with a friend and died in Whangārei Hospital.

And in 2008 13-year-old Daisy Fernandez was struck and killed by a teenage motorcyclist on New Year's Eve as she and a friend sat on the beach.

This week 18-year-old Regan Colin Hutchison Baxter was sentenced to home detention after the ute he was driving rolled and crashed in June, injuring Robbie Cederwall, who died two days later.

On June 24 Baxter was driving a Toyota Hilux at Rothesay Bay, North Shore, carrying seven others - in the cab and on the tray - and was showing off doing doughnuts on the beach. The ute rolled.

Baxter panicked and fled as his injured passengers lay on the sand. He later returned, but 17-year-old Robbie was critically injured. Baxter will serve a maximum one year of home detention, 200 hours' community work and is disqualified from driving for two years.