Homes in Upper Hutt are being evacuated, and a firefighter has been hospitalised as crews battle a blaze in Mount Marua.
The fire broke out at about 2pm, and 15 fire engines plus a helicopter are battling to put it out.
Fire communications spokeswoman Jan Willis confirmed one firefighter was hospitalised from smoke inhalation.
She couldn't confirm the condition of the injured fire fighter.
Ms Wills says a number of homes are threatened.
She says there may also be traffic congestion on State Highway 2, where trucks are on the side of the road.
A nearby resident, who doesn't want to be named, can see the blaze from her living room.
She can see huge flames shooting up, and a helicopter working to try to put them out.
She says the fire is heading away from Plateau Rd, heading towards Upper Hutt.
She understands it is the second fire in the area today.
Peter Walker, a deputy rural fire officer at the Rural Fire Authority said the fire was now "fairly contained".
"But we will have quite an extensive mop-up job to do."
There were no threats to houses around Mount Marua.
Mr Walker said the fire consumed "a couple of hectares of native bush and shrubbery" but didn't burn through any property.
There were still two helicopters in the area battling to fully contain the blaze.
"They are working mainly at the front of the fire and that allows our ground crew to come up from behind," he said.
He said both lanes on State Highway 2 were closed because the helicopters needed a clear passage to fly across the highway to use water from the Hutt River.
"Because they have to dip into the water, they are flying across the road so it's a health and safety issue."