Numerous hotspots have been detected after an aerial check with thermal imaging cameras by fire crews dealing with a big scrub fire in Marlborough.
The fire broke out in steep countryside on the Vernon Station, just south of Blenheim, on Friday night.
Marlborough Rural Fire Authority principal officer Richard McNamara said, to reach the hotspots, the crews faced difficult terrain including extremely steep slopes.
"It is not a place to be going picnicking in, and our crews have to be extremely careful."
The weather was in their favour over the next few days, with some rain forecast, and the hotspots should be out by 4pm, he said.
Two helicopters were helping crews on the ground keep the situation under control.
The fire was thought to have burnt through at least 25 hectares but had not damaged any homes or farm buildings.