Firefighters with chainsaws are felling burning trees, while four helicopter crews and 20 firefighters douse hotspots, as an Arthur's Pass scrub fire battle continues.
They want the 50 hectare blaze on the South Island's Mt Horrible extinguished before tomorrow's forecast nor'west wind hits.
The blaze started more than 30 hours ago - about 2am on Monday - with crews working into yesterday evening to contain it.
Canterbury deputy rural fire officer Bruce James said the fire flared up overnight, burning rapidly in one area and threatening Pylon Gully and a beech forest.
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Firefighters doused hot spots this morning.
"Aggressive action was taken at first light this morning using four helicopters to contain the fire," he said.
"Firefighters now going on to the hill using a 'dig and dump' technique to dig up hotspots for the helicopters to extinguish.
"There are currently four helicopters, two [Department of Conservation] chainsaw operators felling burning spars (trees) and 20 firefighters at the fire, plus support personnel."
State Highway 73 near the blaze was open, with speed restrictions, he said.
The weather was good and the fire was contained.