Thick smoke billowed across the highway, the authority said, causing traffic and rail delays. Motorists were shuttled through the area during breaks in visibility.
No nearby properties were under threat, but residents had been warned of the possibility of evacuations if necessary.
Crews would remain on the scene over night to dampen down any hotspots, as the hot, dry and windy conditions meant the fire could re-ignite at any time, Marlborough's principal rural fire officer Richard McNamara said.
"We hit the fire hard and fast to give us the best chance of getting it under control because the conditions are against us; the nor'westers are due to continue, there's no rain in the forecast and the temperatures aren't likely to drop," he said.
"We're going to need a close eye on things in the days ahead."
The area will be closely monitored for at least the next two or three days with fire crews remaining on stand-by, Mr McNamara said.
"This was one of the worst-case scenarios for Marlborough -- the fire risk is extremely high here and it is only thanks to the swift response of the volunteer crews and the good co-operation with police that we were not facing a bigger emergency."
A specialist fire investigator was expected to arrive in the area tomorrow to ascertain the cause of the blaze.
