The fire has burnt through 5ha of land on both sides of the highway near Waipara, close enough for some power poles to catch alight.
A woman who drove through a section of the highway at the time of the fire said she thought she could have died.
Constance Kipa said she was likely one of the last to drive through before the road was blocked off.
"As soon as we sort of came into it, the car got really, really hot and I wasn't expecting that, and then the smoke came across the front and you couldn't see."
A Fire and Emergency New Zealand (Fenz) spokesperson said the fire was still contained to that size and was under control.
The smoke had calmed down and not a lot of hotspots remained visible, he said.
Mainpower said 12 properties were without electricity because Fanz had asked for it to be turned off for the safety of crews.
Residents who voluntarily left their homes on Darnley Rd have been allowed to return.
This is the second large scrub fire in Canterbury in the past week, just days after a blaze at Kirwee.
Fenz assistant commander David Berry told Morning Report conditions were worse than they had been in the past few years.
A couple of small burn fires people had lit recently had reignited in the wind, he said.
"We've also seen a quad bike had an exhaust malfunction and that's caused a fire in a paddock."
People needed to be a bit more sensible and take care, Berry said.
This included not parking on grass with a hot exhaust.
