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.