UPDATED 5.35PM The investigation into the two fires in the Port Hills has now become a police investigation.

Fire investigator Ken Legat told Newstalk ZB it’s certainly suspicious.

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Mr Legat said police are going to start over and begin the investigation again. He said because a death is involved and because fire investigators can’t determine accidental cause, they have to consider all sorts of things.

It is now in the hands of police.

Detective Inspector Greg Murton said while there has been speculation about the cause of the two fires, no definitive cause for either fire has been established at this time.

Police will not speculate on the cause of the fires until the investigation is completed. It's expected to take some weeks.

Earlier this afternoon, fire investigators were calling for videos or photos of the first fire when it was just starting on Early Valley Road from about 5.15pm - to 5.39 on Monday night.

They were hoping someone in Halswell might have filmed the start of the fire from their backyard.

Newstalk ZB Christchurch host Chris Lynch said investigators are urging anyone with footage or any information to get in touch with police.

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On Thursday Prime Minister Bill English said the Port Hills wildfires could be the result of an arson attack.

Mr English cancelled a full schedule of events to travel to Christchurch and tour the fire grounds with Civil Defence Minister Gerry Brownlee on Thursday.

"I've only had a very brief description of the fire starting in two places at about the same time which, to someone like me, looks a bit suspicious," Mr English said after viewing the area from a helicopter.

"I wouldn't want to jump to conclusions but that seems a bit odd."