The ancient kauri saved by protesters is at risk after contractors moved in to cut it down.

In March, an activist spent three days suspended in the kauri on the property on Paturoa Rd, Titirangi, which resulted in the tree getting a reprieve.

This morning, property owners John Lenihan and Jane Greensmith issued a statement saying they are restarting work on building a house on each of the two sites in dispute because the neighbours have not bought the land as they had promised.

About 20 residents gathered in the street to try to save the tree again.

Police and private security guards hired by the property owners are at the scene.

In the statement, Mr Lenihan and Ms Greensmith said the "resource consents were lawfully granted, and that works could continue".

"It has been nine months since protesters invaded the properties at Paturoa Rd and there has been no response received to the landowners' plan," they said.

"This plan was for those parties involved in the protest to purchase the two properties at a fair market value if they wished to save the tree.

"Auckland Council undertook an unprecedented review of the resource consent process and in June confirmed that the resource consents were lawfully granted, and that works could continue.

"In July, Auckland Council formally acknowledged in a written letter the stress and personal toll the situation has had on the landowners.

"The landowners are now continuing with the works towards building a house on each of the two sites.

"The landowners have subsequently started legal actions and as such are unable to comment further."

Four men put a rope up the tree and said they had been instructed to fell the tree, but were not aware of the background and stopped work to seek further instructions.

Neighbour Winnie Charlesworth said her husband Andrew Maehl was working at home when he saw contractors move on to the property at about 10am.

"He called out, 'What are you doing?'" she said.

"They claimed they were just clearing the dead vegetation, and next thing he saw a rope up the tree.

"He called out, 'Are you taking it down?' They said, 'Yes, we are taking it down.' There's a mulcher on the road and about four guys."

She said the contractors told her husband they were not aware that Mr Lenihan and Ms Greensmith had promised not to cut the tree down after protester Michael Tavares sat near the top of the tree for three days in March.

Ms Charlesworth said neighbours had been under the impression that Mr Lenihan and Ms Greensmith were trying to sell the property. One neighbour made an offer for it, which was rejected, and the Save Our Kauri group had told the owners that they were trying to get a group to fund buying the site.

She said it now appeared that the owners had no intention of saving the tree.

"We believe it's a broken promise," she said.

She said the contractors had stopped work.

"They are concerned about being connected with it and the effect it will have on their business," she said.

Mediator Janet Clews said she had met separately with the property owners and their barrister, and with two groups of the protesters, but had not been able to bring the two parties to even sit in a room together.

"I suggested that, but I don't think there was a mind to do that," she said.

"I'm not sure that it was going to be productive because of the stance of the two opposing views."

She said she was asked to mediate by Auckland Council with clear instructions that the property owners had a valid resource consent to cut down the two trees, and that the council was not in a position to buy the properties.

She said it was "a gross exaggeration" to say the kauri was 500 years old as reported in March because "most of the land was felled years ago".

"It would probably be 200, but it's not relevant, really," she said. "It's a beautiful old tree, but if that [felling it] is the only way that land can be developed, then the owners have certain rights as well."