Marlborough Principal Rural Fire Officer Richard McNamara said it was likely to take at least 24 hours to contain the large forest fire burning through a private forestry block to the north of Marlborough's Wairau River in the Waikakaho Valley.
About 50 fire fighters are at the scene and nine helicopters are fighting the fire from the air. Five of the 24 houses in the Waikakaho Valley have been evacuated by Police.
With the fire burning steadily across slopes of thickly forested land, fire crews are concentrating on protecting houses and forestry equipment in the area.
"At this stage the fire is moving fast and it's too dangerous to put crews onto the burning hillsides but we're hoping the wind will drop tonight," he said.
"It's already moved pretty quickly and is just beginning to spread from a YSI Forestry-owned forest and into Marlborough District Council forest," said Mr McNamara.
Relief crews from outside the district were being called in as conditions were difficult and crews would be needed on the ground for at least another couple of days.
Mr McNamara said the weather forecast for the next few days was for hot, dry, windy weather which would be very challenging for fire fighters.
"There's a lot of heavy fuel in the way of this fire and we're going to need heavy machinery on the job; it's going to be a long, dirty grind," he said.
The fire was reported about 2.30pm this afternoon.
Road blocks are in place at each end of the Kaituna Track between State Highway 6 and Tua Marina.
Waikakaho Road is closed beyond the fire staging area.
Police are assisting with the evacuation.