The Fire Service is worried three arsons in Canterbury overnight are part of a pattern involving unoccupied buildings.
The fires at empty residential properties in Kaiapoi, Bromley and Dallington, caused extensive damage and follow others in the suburbs over the past few weeks.
Two houses and a large woodshed were completely gutted by the blazes in the early hours of Sunday morning.
Christchurch's fire risk safety manager Graham Davies says there is an obvious trend towards arson attacks on abandoned, earthquake-damaged properties and he's worried it could get worse coming into summer.
He says overgrown gardens will dry out, making the fires even harder to contain.
Mr Davies says firefighters have to treat abandoned houses as occupied in case there is a homeless person staying there.
He says this puts firefighters in extra danger because they have to enter the property to check.