Police had a large presence at an anti-1080 protest in Auckland.

Police have blocked a bid by anti-1080 protesters to march across Auckland Harbour Bridge after a confrontation in which two people were arrested.

A "Hikoi of a Poisoned Nation", whose members say they are walking the length of the country to protest the use of the 1080 pesticide, tried to cross the bridge about midday on Saturday.

Protest leader Emile Leaf led several hundred people from Takapuna, on Auckland's North Shore, aiming to walk to Bastion Point.

SUPPLIED Police at the scene of an anti-1080 protest at Onepoto Domain on Saturday afternoon.

However, a wall of police thwarted any attempt to cross the bridge, and it is understood Leaf was one of two people arrested.

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The group expected to cross the bridge around midday and gathered at Onepoto Domain in Northcote, before heading off.

Rachael Kelly/Stuff Hikoi of a Poisoned Nation protesters, from left, Unaru Murphy of Kumara, Allan Gurden of Blackball, Phil Peterson of Hari Hari and Joe Kanara of Greymouth are marching to Parliament to protest the use of 1080.

At least 40 police officers blocked the group's way out of the domain.

"You're refusing our right to protest!" said a protester to a line of police.

Inspector Alisse Robertson said the police had to stop the protest because it was unsafe to themselves and the public, if they were to walk over the bridge.

Supplied Police pulled over protestors on the motorway heading south.

"Their cause is no issue with us," Robertson said. "We offered them multiple options, as had NZTA.

"They walked just fine from Takapuna Strand to here no problem. We gave them the option to walk over the Greenhithe bridge because it's safer," she said.

Robertson said the NZ Transport Agency did not receive a formal application from the group to cross the bridge, and the hikoi had been advised any request would not be approved because of safety concerns.

"The group has chosen to ignore this advice and despite numerous attempts by police staff to look at alternative options, they have refused to negotiate."

She confirmed two people were arrested on charges of assaulting police and obstruction.

The protesters eventually drove over the bridge in cars and vans, although police stopped some of the vehicles, apparently asking them to remove signs and flags.