There is no contingency plan if the fires are not under control by the time helicopters and planes have to stop fighting it at nightfall.
Selwyn principal rural fire officer Douglas Marshall said the goal was to contain the fires by tonight.
When asked by the Christchurch Star what would happen if the blazes were still out of control by nightfall, he said: "The goal is to contain it by tonight. At the moment there is no contingency plan - you'll have to ask me that in three hours."
Helicopters and fixed-wing aircraft have to stop flying at nightfall because of the dangers of power lines.
The fire was believed to have been contained by nightfall on Tuesday, but flared up again overnight.
Strong easterly winds have caused havoc on Wednesday, with evacuations in Worlseys Rd, and Kennedys Bush.
People living in Westmorland have been advised to prepare to move out. Many are.
Fourteen helicopters and two fixed-wing aircraft and 120 firefighters are trying to contain the blaze.
Marshall said if more resources were needed he would look at it.
Meanwhile, Marshall says the decision to bring helicopters in to fight the fire on Early Valley Rd was not made too late.
More than one affected resident said they were concerned that not calling in helicopters straight away may have allowed the fire to grow to the size it did.
Marshall said the matter would be reviewed at the end of the operation.
"In the heat of the moment we often get those comments that things perhaps could have been organised sooner and part of our review will have a look at that," Marshall said.
"At this time we are comfortable that we did call the resources appropriately and it's something we will look at and just check as part of our own processes in making sure we have done things right."
He couldn't immediately say what time helicopters were called in but didn't believe a chance had been missed to stop the fire getting as big as it did.
"There is always a combination of factors with fires and fires on hills are always challenging because of the terrain. Although helicopters have been our principle firefighting attack today, often ground crew can be more than adequate to meet the initial demands."
One of those concerned was evacuated Holmes Rd resident Graeme Causer who told media yesterday that if helicopters had been brought in earlier and locals' advice had been heeded, the fire might not have spread so far.
An Early Valley Rd resident, who declined to be named, said that while he was away on holiday in Northland when the fire started he was concerned at hearing reports that helicopters were not called in soon enough.
He was also disappointed that the Selwyn District Council did not have a water main going up the road which could be used by firefighters.
Marshall said the matter of the water main was something that could be looked at and followed up on.