A fast-moving grass fire near Bredbo forced the closure of the Monaro Highway on Friday afternoon.
Livestock were moved onto the highway to save them from the blaze.
A lightning strike started the fire at about 1.30pm, three kilometres south of Bredbo, which threatened the communications tower on Cosgrove Hill, and a homestead.
Cooma police Sergeant Richard Nicholson said the highway was closed for about an hour.
"The highway was closed initially to preserve stock," Sergeant Nicholson said.
"They had nowhere to go, so they were pushed onto the road to get away from the fire."
Sergeant Nicholson said the highway remained closed until the thick smoke cleared.
Rural Fire Service Inspector Rein Peet said there was lightning in the area at the time and eyewitness accounts that it was the cause of the fire.
By coincidence, a RFS volunteer almost saw the fire start and quickly called for help.
Colinton Brigade senior deputy captain Nick Goldie was on the scene at the time the fire started.
"I was driving home (south) from Cooma at lunch time on Friday with a car full of groceries, and was watching one of those odd little isolated storms, a sort of black lump of cloud above Bredbo," Mr Goldie said.
"There was one huge bolt of lightning, which seemed to reach the ground near the communications tower.
"By the time I reached the 'rabbit farm' I could see the hilltop opposite was blazing. So I called fire control on the radio."
The Bredbo fire brigade was first on the scene joined by the Colinton brigade.
Fire crews attacked a long fire front blowing to the south from the initial lightning strike.
A dozen or so RFS fire trucks rushed to the fast moving fire including a Fire and Rescue NSW (FRNSW) tanker and RFS brigades from Cooma, Michelago, Jerangle, Dry Plains and Shannons Flat.
In all, 16 fire trucks, two graders and two bulk water carriers were needed to deal with what has been called the Cosgrove fire, just south of Bredbo.
Mr Goldie said the western flank of the fire was contained along a grader line parallel with the highway, which allowed the property owner to move stock to unburned paddocks.
Some 400 hectares of African Lovegrass were burned including some bushland, but fortunately there were no stock losses, and one threatened homestead was safely defended.
FRNSW Cooma brigade captain Chris Reeks said the Cooma FRNSW bulk water tanker was called on to defend a house near the river.
"The fire moved very quickly and threatened the house," Captain Reeks said.
"We were there from 2pm until about 10pm."