A group working to save native trees in the Auckland suburb of Avondale say the remaining trees were poisoned last night.
Native trees on the corner of Canal Road and Wairau Avenue in Avondale are due to be chopped down, after the section was sold to developers to build houses.
Mana Rakau has been protesting at the site for 224 days to save the trees.
Spokeswoman Juressa Lee said about midnight last night a man snuck into the site and drilled poison into 18 of the trees, including a rare kawaka, before being scared off my a member on night watch.
With arborists, the group had a strategy to remove the poison and remediate the trees, she said.
Police are also investigating the damage to the trees.
They said damage to the trees was consistent with them being drilled, and they were making further enquiries.