The fire on the Tiwai Peninsula in Southland has been contained, Fire and Emergency says.
The fire grew to 1200 hectares in hot, windy conditions on Thursday, but was contained by the end of the day and did not grow in size overnight.
Incident Controller Hamish Angus said despite warmer conditions Friday afternoon, firefighters had been able to hold down any potential flare-ups.
Angus said there were 35 firefighters on site on Friday, with support from five helicopters, the Department of Conservation and local forestry companies.
The fire was burning scrub and valuable conservation wetland, with a perimeter of 18 kilometres.
Four helicopters were dousing the fireground from above and excavators are widening firebreaks around the perimeter so the fire didn't spread if the wind picks up.
"This work will also help firefighters if they need to deal with any more fires here in the future."
Crews will work until 6pm, with one to remain overnight and monitor the fireground. They will then return to continue the mop up in the morning.
"They've all worked incredibly hard over the last two days, and done a great job at getting such a large vegetation fire under control."
The fire posed no immediate threat to people, homes, the Tiwai Point smelter or the Tiwai Bridge, Fire and Emergency said.
Angus earlier told Morning Report the outlook was "pretty good".
"We just had a bit of a look up there this morning and,, things look pretty contained and controlled. We haven't got any visible flames at the moment, so things are looking really good."
It was too early to determine a cause just yet, he said.
"We've got a couple of fire investigators coming out here this morning,, so I'm sure we'll get to the bottom of all of that."
Cooling pumps for the aluminium smelter were threatened by the blaze, but they had been so far protected.
"Tiwai is well used to this - certainly this isn't the first fire down here, so they do have other options [for] generation… It wouldn't have been a catastrophe, but certainly one of their priorities today is supporting the power contractors to get in there and get the lines connected to pumps."
The primary job now for firefighters would be establishing a "cold perimeter" and knocking out any heat sources before the wind picks up, forecast for later in the week.
"It's pretty much time now for the real grunt work to start."
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