Police are setting up checkpoints north of Auckland to stop people fleeing the city.

But the clampdown is also making it hard for coastal residents to get food and essential supplies.

The three new fixed checkpoints are being set up at the northern limits of the Auckland region on State Highway 1's intersection with SH12, Mountain Rd in Kaiwaka and at Cove Rd by Bream Tail Rd.

Northland police had earlier been setting up temporary checkpoints and patrolling the region to ensure motorists were only driving for essential reasons.

Since New Zealand was plunged into lockdown, Kiwis have only been allowed to leave their home to shop for groceries or visit a GP or pharmacy or to get a Covid test or vaccine.

The only other reason to leave was if they work in an "essential" job and are on their way to returning from work.

"Anyone attempting to travel into Northland from outside of the region or around the region can expect to be stopped by police at a checkpoint or randomly, and asked about their purpose for travel," Northland District Commander Superintendent Tony Hill said.

"We have now been under alert level 4 for a week, and there's no excuse for people not following the rules. "

However, residents living near coastal Mangawhai have reported being turned away at the checkpoints while on the way to collect their post or visit supermarkets.

One Herald reader said his wife was turned round by the police while trying to get to Mangawhai Heads from their home in Langs Beach to buy food supplies from the town's Four Square, which is their nearest supermarket.

As well as being turned back from the supermarket, they also couldn't get their mail, he said.

"We now can't get our post either, as we get no home delivery and need to visit our PO Box in Mangawhai Heads post office."

The police told the man's wife they were trying to stop people escaping Auckland.

"But when my wife pointed out that the border is south of Mangawhai Heads, the police said they were at the district health board border," the man said.

Another Mangawhai Heads resident said the town "has been effectively locked off by police today".

The checkpoints meant residents were not able to go south to Warkworth or north to Ruakaka to get to the two closest larger supermarkets.

"We can't currently get supermarket deliveries so are being forced to shop at dairies," the man said.

"Police are saying it is due to too many people from Auckland heading north."