Eleven people have been told not to return to their homes tonight as firefighters keep an eye on a large scrub fire near Hanmer Springs.
The Fire Service said the fire was contained, but there was a chance it could flare up again.
State Highway 7 was closed between Culverden and Hanmer Springs - blocking part of the current main route from Picton to Christchurch - from about 2pm.
The cordons were lifted at 8pm, but there was a speed limit of 30km/h.
The New Zealand Transport Agency advised drivers to keep their car windows closed, as it would be smoky.
Watch a video taken by Christchurch businessman Jeremy Thomas before the highway was closed:
Hurunui principal rural fire officer Allan Grigg said 11 people had left their homes. Three fires were burning on both sides of the highway, spread over 60 hectares in two plantation blocks.
No homes were thought to be in danger.
Eight helicopters, 12 ground crews of about 40 firefighters and heavy machinery were involved in the operation.
The alternative route between Picton and Christchurch is via State Highway 73, the Arthur's Pass/Otira route. Under normal conditions, this would add about two hours to the journey.
Earlier this evening, dozens of cars and freight trucks were in a queue at a cordon near Culverden. Police were allowing restricted access for residents.
Australian tourist Daryl Judge, who said he used to be a firefighter in Sydney, was among those in the queue. "We can see the plumes of smoke coming up," he said.
Power to 50 properties around Lewis Pass was switched off as a precaution. It might not be restored until tomorrow, as workers needed access to the area to assess any damage, a MainPower spokeswoman said.
North Canterbury has experienced drought-like conditions for about three years.
SH7 became the main South Island thoroughfare after the Kaikōura earthquake forced the closure of part of SH1.
'It was just a massive ball of smoke'
Firefighters ramped up their efforts late this afternoon, increasing resources from the initial seven fire crews and four helicopters.
Three of the helicopters had been diverted from doing sluicing work on the earthquake-damaged SH1 in Kaikōura.
The blaze was a few hundred metres from Hamish McRae's home on the Lochiel Station farmstead. He said things were a bit hairy for a while.
"It got into about 20 hectares of pine trees... they managed to keep it off the main hill," he said. "It was just a massive ball of smoke."
Look closely at the middle of this gif, you can see the smoke plume developing from a fire near Hanmer. ^AH pic.twitter.com/zpPWYULw6E— MetService (@MetService) March 1, 2017
People who could delay their journeys today were advised to do so.
Have you been affected by the fire? Contact RNZ at firstname.lastname@example.org