We called 111, cyclists say

Two cyclists who were sought by police after they were filmed near the scene of a large fire near Arthur's Pass say they called the fire service as-soon-as they saw the flames.

The fires, on State Highway 73, subsequently spread to burn more than 300 hectares of land at a high country station.

A motorist filmed the initial fires and those using the road at the time, including the cyclists and a tractor driver.

Police said they were trying to get in touch with the cyclists and they had now identified them.

But a cycling page on Facebook page quoted the cyclists as saying they sought emergency help as soon as they saw the fire.

In the statement, they said they raced to the top of a nearby hill to get cell phone coverage and called the fire department immediately, then left the area straight away.

"We have no TV or news at Castle Hill Village where we were staying so we went out on our 6hr ride the next day not knowing police were looking for us!

"We assumed they would have known what happened! But we made our statements last night of what we saw.

"We still can't believe we saw it happen right in front of us and how fast it spread," they wrote in the statement.

The cyclists did not reveal their identity on Facebook.

Police also said the tractor driver had contacted them.

Fire safety investigators would now talk with the driver and the cyclists as they seek the cause of the fire.

The Department of Conservation (DOC) earlier said the fire was contained and crews hoped to have secured 80 percent of its perimeter by the day's end.

However, a hot, windy afternoon had set firefighters back in their battle to control the blaze and helicopter, plane and fire crews are still working to try to contain it.

Crews work to circle fire

Fire crews have been attacking the fire on the ground after two days supporting aerial water drops.

The fire started on Monday afternoon on the Flock Hill Station side of State Highway 73, opposite Craigieburn Forest Park. The 330-hectare blaze was now contained but still burning.

Crews have been working to create a cool zone up to 20m deep around the fire's perimeter.

Most of the firefighting effort over the past two days has been from the air, because the flames were too fierce to get near, but today up to 40 firefighters have been deployed on the ground.

Helicopters with monsoon buckets were still operating and planes capable of carrying fire-retardant chemicals remain on standby throughout the day.

DOC technical fire support officer Craig Alexander said cool temperatures and some drizzle were helping keep the fire under control.

He said firefighters were working systematically around the 8km perimeter of the blaze to ensure it did not spread but it would be some time before the fire was completely out.

"It's going to be weeks. There's the possibility of using the thermal camera on the site to locate those few invisible hotspots and then we'll systematically work with those and put it out."

Trees were being felled to make sure water being dropped from the air could get to the ground.

Speaking shortly after a briefing this morning, incident controller Bruce Janes said everything was in place for ground crews to attack the blaze.

"They are going to give us this perimeter, this perimeter security - a 15-20m blackout zone right around the whole perimeter," he said.

"Knocking down spars and putting out hotspots - digging them up, bombing them with helicopters or just pumps or just hand tools."

Mr Janes warned the fire could revert to a massive blaze almost instantly.

"Give us one hour westerly in hot temperatures - 100 percent back where we were. Fire whirlies, potential breakouts, a big tall spar burning away on its top - that can blow an ember right out of the fire ground, transport it some distance."

Mr Janes said they would only be in the clear after an inch of rain or six weeks without fire.