Two cyclists and a tractor driver could hold the key to working out how a massive scrub fire started near Arthurs Pass yesterday.
Ten helicopters have been battling the blaze that broke out at around 2.30pm.
The fire had spread to almost 500 hectares near State Highway 73 and closed the main road between the West Coast of the South Island and Christchurch.
Now, Canterbury police are appealing for the cyclists and tractor seen on State Highway 73 travelling towards Christchurch near Flock Hill where the fire started to come forward.
"This fire appears to have started in four separate locations along the east-bound bank next to SH73 yesterday," said Detective Inspector Greg Murton.
"A member of the public has provided police with dash-cam footage that shows two cyclists close to where the fire is believed to have started.
"We are keen to talk to them as they are key witnesses and may be able to provide us with information that can help with our inquiry.
"We understand that a tractor had also recently driven past the area and are keen to talk to the driver also."
Mr Murton said there had been considerable damage to surrounding paddocks and bush.
Anyone with information on the fire can phone police on 03 363 7670 or provide information via Crimestoppers on 0800 555 111.
A skeleton ground crew worked to stop the fire spreading last night.
The Department of Conservation has now taken over the fire fighting efforts.
Castle Hill Community Association chairman John Reid said the local community was prepared for evacuation.
An emergency response team has been set up and visited those who have stayed behind.
There are around 30 people left, including visitors, at the village which has 125 houses and around 20 permanent residents.
However, Mr Reid said he drove near the site of the blaze this morning and thought the chances of being evacuated were now remote.
"There's no wind and it's a calm day up there, thank goodness," he said.
"If there had been a big nor'west wind blowing there would've been problems."
There were no houses or farms currently in danger, he said.
It's been an extremely hot and dry summer for many parts of the South Island.
The scrub in the Arthurs Pass area is parched and brown.
Mr Reid, however, has lived in the area for more than 40 years and it's the first major scrub fire he can recall.
