Ten of the eleven houses destroyed in the Port Hills fire could have been saved had career firefighters not been sent home at the start of the blaze, union bosses say.
Derek Best of the NZ Professional Firefighters Union said he has been told by career firefighters they were told to go home by Rural Fire officials after helping contain the fire on Monday night.
"Initially there was a response by our people to the incident, and then they were told you're not really needed any more go home go back to the station," Best said.
An hour and a half later fire crews were called back to the scene as the fire had spread again.
"It really upset them," Best said.
"They were unable to deploy and they could see the flames from the station and they weren't able to go back."
He said career firefighters did not leave a scene until a fire was out, whereas Rural Fire officials worked to contain a fire but not necessarily put it out.
"Our people had contained the fire and were told to go back to the station and as soon as they did that the fire got away again.
"Ninety minutes later they were called back instead of coming back to a contained fire, which is what they left, they came back to an inferno," he said.
"They had to start all over again."
Late tonight, a joint statement was released by the emergency operations centre public information management team on behalf of the Fire Service's fire region commander, Steve Turek, and Selwyn District Council's principal rural fire officer Douglas Marshall.
They acknowledged that the Port Hills blaze had been "one of the most complex in recent years'' and meant both urban and rural firefighters turned out.
"All firefighters have worked very hard in tough conditions,'' they said.
"In incidents of this size and nature, rural and urban firefighters will respond together. Decisions are made under a clear command and control structure amongst rural and urban fire officers based on a number of factors - but there is always a clearly agreed lead on all fire grounds.''
Turek and Marshall said safety was a key factor in determining where crews were placed.
"In the Port Hills fires, terrain, wind conditions and heat intensity have meant extra caution must be taken around how close firefighters can be to the fire.''
They said all fires had an operational review undertaken after the blaze had been fully extinguished.
"The purpose of that review is to evaluate the response and identify any opportunities for further improvement.
"For now, our focus is on putting out the fires.''
Best said career firefighters had told him with confidence they think 10 of the 11 homes destroyed in the days since could have been saved if they had stayed on the first night to totally extinguish the flames.
"What our people are telling us is if they'd been fully deployed we wouldn't have lost any houses. That's their best estimate based on experience."
Best was calling for an independent inquiry into what had happened, saying there were questions about who should have been in command and whether lines of command were clear as the incident unfolded.
"It's got to be looked at properly," he said.
"You can't deal with this in any other way than having a whole independent inquiry."
Selwyn Rural Fire officials are being sought for comment.