Unique conditions yesterday meant a blaze which tore through more than 4600 hectares of grassland and scrub in Otago was spreading five times faster than normal, Otago's top rural firefighter says.
The fire erupted near Te Papanui Conservation Park, near Middlemarch, yesterday morning.
A hot and windy day helped fan the flames yesterday and by nightfall it had burnt through 2773 hectares of grass and scrub.
The blaze continued to spread overnight and tore through more than 4600 hectares of land before rain and low cloud helped bring it under control this morning.
About 15mm of rain fell in the area.
Fire and Emergency's principal rural fire officer for Otago Graeme Still said although firefighters yesterday had a plan to tackle the blaze, conditions were challenging.
"Some of the winds we had to deal with were blowing up to 100 kilometres an hour, [there were] very warm temperatures and no vehicle access," he said.
"The fire at its peak was advancing about one-and-a-half kilometres an hour. That's very fast. Just to put some perspective on it they normally run about 300 metres an hour."
However, it is now under control.
"I'm pleased to say that the fire's contained. I'm not pleased to say that our mapping shows that the burnt area is around 4664 hectares. About 1100 hectares of that is [Department of] Conservation estate and most of the rest of it is owned by the Dunedin City Council."
A small area near the Meridian windfarm was owned by the Clutha District Council, he said.
More than 50 firefighters remained at the fire ground today, though that number would swell to 90 tomorrow when thermal imaging would allow crews to better identify hotspots.
Thermal imaging could not take place today as it was not safe for aircraft to fly due to low cloud, Mr Still said.
Four ground crews and 11 helicopters fought the fire at its peak yesterday afternoon.
"I'm pleased to say we managed to save one house and prevent damage to the Meridian windfarm," he said.
"We believe that one shed was destroyed, but we can't confirm whether any other structures have been damaged at this stage."
Main water source contaminated
Dunedin Mayor Aaron Hawkins said residents would need to continue to conserve water.
The city's main water source, Deep Stream Reservoir, was contaminated by fire retardant during firefighting efforts.
The reservoir is normally the source of about 80 percent of the city's water supply.
"We are still asking residents to voluntarily conserve water while we assess the implications for supply in the medium term," Mr Hawkins said.
"At this stage it seems likely those voluntary restrictions will remain in place over the summer. We may have to consider more formal restrictions based on the weather and water usage over the coming months."
While it was inconvenient, it could have been much worse.
"This is a significant event, there's no doubt about that, but it could've turned out much worse," he said.
"On behalf of the city we'd like to thank all of the Fire and Emergency personnel for their efforts to contain and suppress this major fire both on the ground and in the air.
"Thanks to these efforts and the very welcome rain today we can be pretty confident one of our key water catchments - Deep Creek - is unaffected by the fire. We should have confirmation of this tomorrow."
Mr Still said a fire investigator would arrive at the location tomorrow morning to determine the cause of the blaze.