The fungal disease kauri dieback may have spread south to Waikato.
The regional council says two kauri trees at Woodstock Primary School in Fairfield have been cordoned off after a member of the public spotted symptoms of the disease.
Kauri dieback is currently only found in Auckland and Northland and eventually kills the tree after entering through the roots.
Tests will be carried out on the trees and results are expected to take six weeks.
The trees were planted at the school about 40 years ago.