Fire bosses are deeply concerned with a spate of seven fires at Christchurch's Bottle Lake Forest Park.
The last fire, near Landfill Ave at about 5.15pm on Monday, spread 20 metres over forest ground.
It took four crews an hour to extinguish.
Fire and Emergency has yet to establish if there is a link between them over the past month.
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Senior officer Bruce Irvine said the risk of another fire spreading and endangering life and property increases, as Canterbury continues to dry out.
He said they're working with partners to look at ways to reduce risks in the area.
A police spokeswoman said their investigation is ongoing.