Firefighters are trying to strengthen containment lines around multiple blazes in Kaikōura before the wind picks up this afternoon.
The fires, fanned by fierce winds, have destroyed 14 buildings, including five houses, but firefighters were able to save another five homes.
Eleven crews, including heavy machinery, two helicopters and dangerous tree fellers, are fighting blazes across a large area of Kaikōura Flats.
Assistant National Commander Ken Cooper this afternoon said people in the Kaikoura Flats area who hadn’t been evacuated must remain vigilant of spot fires and report any immediately.
"We need your help to keep on top of any new fires that might start as the wind picks up this afternoon through until tomorrow," Copper said.
"In addition, we are asking every landowner, agricultural contractor, forestry manager and lifestyle block owner to help us avoid any more fires starting, and please check any old burn piles to ensure they are fully extinguished."
Fire crews are preparing for winds to exceed 100kmh in places, along with high temperatures and low humidity.
Fire and Emergency New Zealand this afternoon confirmed evacuated residents in Kaikōura can return to their homes from 5pm today.
"People must remain vigilant and be prepared to leave if the situation escalates further," the Kaikōura District Council said, in relation to the move.
Earlier, Incident Controller Dave Key said there were "a number of dangerous trees".
"They're burning from the inside out so that's a priority for us and really strengthening our containment lines while we've got this small weather window before the wind picks up this afternoon and more again tomorrow," .
While the fires continue to burn, there was some good news for travellers this morning - State Highway 1, which was closed overnight between Ward and Kaikōura, has reopened.
Fire and Emergency New Zealand (Fenz) said this morning it had crews on the ground and planes and helicopters in the air to bring the fires under control.
"We've got a lull in the weather today that's allowing us to fly our helicopters and extinguish that fire," Assistant National Commander Ken Cooper said.
He said crews yesterday responded to six vegetation fires, and it was three of those that had damaged property.
"There are a number of fires that have been lit in the open over the last number of days that weren't properly extinguished and the wind obviously fanned those and caused those fires to reignite," Cooper said.
One was driftwood on a beach being used as a bonfire, another was a shelterbelt.
He said it wasn't clear if any of the lit fires were the ones that had damaged the structures and homes.
There was now a race to put the fires out ahead of more severe weather forecast for Thursday.
"What we're really trying to stress going forward is really imperative - that we get across to everyone is that we have a significant event coming in from midnight," he said.
Key said they were preparing to ramp up resources and call in firefighters from further afield if needed.
He asked people in Kaikōura Flats to be vigilant and report any fires in the area.
"Definitely when you have high winds, the fire does tend to spot so it can start another fire 500, 1000 metres downwind," he said.
Takahanga Marae in Kaikōura was open for evacuees, he said.
Key this afternoon said it was way too early to work out how the fires started, but fire investigators had arrived.
Evacuees were getting managed entry to their properties, handled through local officials, to check on their properties and livestock.
"That's a priority for us as well ... making sure that cattle and sheep get watered in the meantime," he said.
Meanwhile, Kaikōura will be under an orange strong wind warning from 6am tomorrow with severe gale northwesterlies expected to gust 130kmh in exposed places.
MetService said there was a high chance it would be upgraded to a red warning. Red warnings have been issued for other parts of Canterbury.
Mayor Craig Mackle said his thoughts were with people who had lost property.
"Fortunately, there have been no injuries or fatalities reported at this time," he said.
He thanked fire officials and police, saying they were doing an outstanding job as they worked to contain the fires.
More than 900 properties are without power in North Canterbury as a result of strong winds, mainly around Kaikōura
MainPower is assessing damage but says people should prepare for power to potentially be off for several days.
MainPower is assessing damage and prioritising reconnecting the main power links along State Highway 1 in Kaikōura.
"We are asking people that they may need to prepare for the fact that power may be off to their properties for several days and maybe longer," council chief executive Will Doughty said.
All water supplies apart from Clarence and Fernleigh are back on, but people should conserve water.
There are multiple local road closures and anyone travelling should be vigilant for hazards on the road due to fires and wind downing trees.
RNZ reporter Keiller McDuff, who is in Kaikōura, earlier said it was not yet known how the fires started.
However, once they started the high winds created "a bit of a disaster" in terms of spreading dozens of fires.
"The fire ground is incredibly dispersed."
It was difficult to know how big the fire ground is. Some people had gone up in helicopters in very testing conditions to try and survey the scene.
It covered a wide swathe of the northern part of town and jumped State Highway 1.
"We tried as hard as we could but just couldn’t save them all."
There were also fires in the southern part of Marlborough and some fire crews on their way to Kaikōura had to turn back to deal with those.
Winds also allowed the fires there to spread.
About 30 appliances stayed overnight, the crews mainly protecting other structures.
State Highway 1 near Kaikōura was closed overnight because of the fires, but reopened about 8.25am. However, other highways remain closed.
Fallen trees are blocking Inland Route 70 which is closed from Peketā south of Kaikōura to Waiau.
Flooding has also shut the Lewis Pass (SH7).
Meanwhile, some highways are closed in the North Island after strong winds and heavy rain caused major disruptions, and power remains out to thousands of people in Wairarapa.
Four vegetation fires continue to burn in Pōrongahau in Hawke's Bay.
Firefighters have been monitoring the fires overnight - and operations were expected to resume at first-light.
Around 50 to 60 firefighters are expected back today.
