The newly installed automatic gate at the entrance of Maungakiekie / One Tree Hill on Manukau Road has sustained significant damage, leaving it inoperable.
Tūpuna Maunga Authority said, after initial inspection, the gate is believed to have been hit from the front between 2am and 4am.
It would take about two weeks to install a replacement gate.
Tūpuna Maunga Authority chair Paul Majurey was disappointed.
"The Tūpuna Maunga are wāhi tapu to mana whenua and should be safe spaces for all our community to enjoy. These types of actions cause frustration to all of us that [sic] cherish these taonga."
The Tūpuna Maunga Authority have filed a police report and said security would be increase till repairs were completed.
Anyone with information about what may have happened at the scene is asked to contact police or Auckland Council.
In a statement, Auckland Council said the gate was there to protect the maunga from vandalism, thefts, and anti-social behaviour after hours.
It was actioned after the copper dome roof on Stardome Observatory was stolen causing $200,000 worth of damage.
The Tūpuna Maunga Authority has also installed automatic gates at Takarunga / Mount Victoria, Maungarei / Mount Wellington, and Ōwairaka / Mount Albert.