Police are investigating suspicious fires in Patea on Christmas night and in the early morning of the following day.
Patea firefighters were called to a fire burning under a classroom at St Joseph's Convent School at 10.19pm on December 25, Chief Fire Officer Grant Hurley said.
It "took a bit of putting out", but the classroom suffered only smoke damage.
Firefighters were called again at 5.17 the next morning, to find a fire burning under St George's Anglican Church, a Category 1 historic building registered with Heritage New Zealand.
It was extinguished.