"They're going through using handsaws and pumps and hose, and also chainsaws to cut things that need to be cut, just incase there's burning inside trees."
The dampening down process would continue throughout today and tomorrow, he said, with crews working to "put a fence of dead, burnt ground around the fire".
"It's all steep, hazardous terrain, they're not going to work around it in a day. If they get a kilometre or two today, that's great.
"But they'll be working through there to make sure that's contained as much as possible, and then moving on to working on the ones in the middle."
Tomorrow morning a thermal camera would be used to locate any hot spots still remaining, Mr Alexander said.
The camera could identify "golfball sized embers" in the burnt black scrub, which appears extinguished to the naked eye.
The fire, at Flock Hill near Craigieburn Forest Park, was the 105th blaze on DoC controlled land in the eastern South Island so far this year, Mr Alexander said, urging people to be more vigilant in fire-ban areas. A "high average" for a normal year was 87, he said.
"Most of them are small ... but we're in a prohibited fire season throughout Canterbury and things are, it's quite right to say, explosive," he warned.
"All the way from Mackenzie, throughout Otago, up into Nelson-Marlborough, things are hideous."
Fire authorities were on "serious watch" for any outbreak, no matter how small, he said.
"As this one shows, they start small but they can get to hundreds of hectares. So we would like to remind people just to be very, very cautious."
DoC said the Acheron Road through Molesworth Station will be closed to vehicles from 7pm tonight due to the fire risk.
DoC manages Molesworth and said early closure of the road was necessary to protect the station's working farm and outstanding natural and historic features from fire.
If the fire risk reduces sufficiently the road may re-open during the current open season, which ends on April 12, DoC said.
DoC Renwick Partnerships Ranger Clare Moore said: "Movement of people and vehicles through the station increases the risk of a fire starting and fire could cause serious damage to the station's cattle farm, its rare native plants and animals and its historic buildings."
Yesterday, police said the Arthurs Pass fire appeared to have been started in four separate locations along the eastbound bank next to State Highway 73, which is the main road between the West Coast of the South Island and Christchurch.
Two cyclists and a tractor driver, spotted on dash-cam footage close to where the fire was believed to have started, have been identified and would be interviewed by the Fire Service as part of their inquiries.
