A park ranger living on the doorstep of Christchurch's Bottle Lake Forest Park says a spate of fires in the area is the worst he's seen in three decades.
Authorities, locals and the Christchurch City Council are on high alert after seven fires were deliberately lit in the area in just under a month.
The popular walking and biking spot north-east of Christchurch is visited by a million people a year and now the public are being urged to be vigilant and help solve the mystery.
Warren Hunt has spent close to 30 years living on site as one of two Bottle Lake Forest park rangers.
He said he's shocked and saddened by the suspicious fires.
He guided me through the forest clearing to show me an area of the worst damage. The pungent smell of pine trees burnt to a crisp hit us straight away.
With the most recent fire lit only on Monday, the forest's tinder dry conditions meant fires would only grow in size within the close to 1000 hectare pine plantation.
Fire and Emergency Senior Officer Bruce Irvine and his team are on high alert and are investigating the fires alongside police.
"This is causing significant concerns. Each fire is getting larger because the forest is starting to dry out. We are trying to identify and prevent these fires from happening in the future."
The public is being asked to come forward with any information and to call the police non-emergency line 105.
Appeal to nearby residents
Irvine also asked concerned residents living nearby to trim their trees, keep grass low and watered around properties to prevent any future fires from spreading.
Residents who did not wish to be named, said despite the low risk to property, they're still worried.
One man said: "I'd be silly if I wasn't worried, we have lived here for 41 years and it hasn't been a problem before."
Another resident said: "I'm concerned every time I smell smoke. We were just talking last week, if a spark were to fly onto our hedge... we're thinking of cutting that hedge out."
Meanwhile, Hunt is desperate to see his beloved backyard left in peace - for everyone to enjoy.
"We are knocking on a million visitors a year. People are hugely passionate about it. I like to think of it as the lungs of Christchurch. It is a sustainable forest and such a good place to come and recreate."
Irvine said a restricted fire season is being considered as Canterbury continues to dry out with warm temperatures expected over most of Labour Weekend.