The Tongariro Alpine Crossing and Northern Circuit are currently impacted and will remain closed tomorrow.
At this stage, the fire has not reached any tracks or huts, Coutts said.
State Highway 47 is closed between the intersections with SH48 and SH46.
Motorists are advised to avoid the area or delay travel until detours are available.
“Crews from six fire brigades plus a command unit are at the scene or on their way, and three helicopters with monsoon buckets are working, with a fourth being used for aerial observation,” Fire and Emergency said in a statement.
It is not yet known how the inferno started.
Colin Baker, who owns and operates Ruapehu Scenic Shuttles, told the Herald the fire appears to be spreading quickly through the dense bush towards the Mangatepopo valley.
Baker said he first saw the fire, which he described as being big at the time, around 3pm and alerted Fire and Emergency.
“It was originally about 200 by 100 meters, kind of area and it just it’s just expanded”, he said, “it was at the side of the road initially.”
Baker, who said he used to work in the fire brigade, described the blaze as concerning, “it’s going to be a really difficult one to get under control”, he said, because of the dense bush and hot, windy conditions.
“The last several days it has been really dry and the sun is so vicious this year [...] now we’ve got a big fire”, he said.
“That’s a worst nightmare fire.”