On the third day of battling the flames, the major incident status was de-escalated at about lunchtime on Sunday.
Firefighters moved to working on extinguishing hotspots.
The Northern Ireland Fire and Rescue Service (NIFRS) has indicated they hope the operation can be wound up within hours.
Thirty firefighters and four appliances arrived at the Co Down peaks at first light on Sunday.
Health Minister Robin Swann visited the scene in Newcastle, Co Down, later in the day.
He met with firefighters and other emergency responders.
“While the situation is improving, the blaze is continuing to cause significant damage to the Mourne Mountain area,” he said.
“The bravery, commitment and determination of these firefighters have very much shone through as they worked tirelessly in extreme circumstances to bring this fire under control. I pay tribute to each and every one of them.”
Firefighters’ efforts have been supported by police, Coastguard, Mourne Rescue Team, Forestry Service, National Trust, NIEA and Sky Watch Patrol.
Coastguard helicopters from the Republic of Ireland and Great Britain allowed fire chiefs an aerial view of the blaze to help inform tactics, transport personnel to remote locations and plan resources.
Chief fire and rescue officer Michael Graham said the minister had seen first-hand the fantastic ongoing effort from firefighters tackling the huge wildfire.
“The minister, and the entire community, have been very supportive of our efforts over the weekend and I know everyone in NIFRS is extremely grateful for that support,” he said.
“This has truly been a multi-agency approach.”
Local people and businesses have been providing food and support.
NIFRS asked that this stop on Sunday afternoon as the operation was scaled back.
Assistant chief fire officer Aidan Jennings thanked all for their support and firefighters for their hard work and resilience in “extremely difficult conditions”.
“Your dedication and commitment in working tirelessly to resolve this incident and maintain our response across Northern Ireland during this period is at the very heart of what it means to be a firefighter,” he said.
He added his thanks to local people and businesses for food and refreshments: “Your support has been a great source of encouragement for our firefighters and partner agencies as we work to resolve this incident.”
Heather McLachlan, the National Trust’s regional director for Northern Ireland, described a very sad day as she surveyed the damage to the landscape from the fire.
“A lot of our land has been impacted by the fire, from Thomas Mountain through to Millstone Mountain over to Donard,” she said.
“It’s a bit of a lunar landscape and still some of the peat bog is smouldering.
“A very sad day for all of us and we’re going to have quite a lot of work to do to look at what the restoration might look like for us. We’re going to work with colleagues across the National Trust who have experienced these things before and make sure that we get their expertise and wisdom in how we can help this site move forward.”
On Saturday Mr Jennings said it is “undoubtedly one of the most challenging gorse fires firefighters have ever had to deal with”.
He said fire crews will be available to those who need them despite the operation in the Mournes, but asked the public to be extra fire aware.
“I want to reassure everyone that we have put contingency measures in place and if you need us in an emergency we will respond,” he said.
“However, I am asking everyone to be extra fire aware at this time both in your home and in particular in the countryside.”
The blaze in the Slieve Donard area started in the early hours of Friday.
The Northern Ireland Fire and Rescue Service declared a major incident on Saturday.
here is no indication yet of how it started.
Dramatic images of the mountains ablaze sparked concern, with First Minister Arlene Foster tweeting: “This is devastating and tragic. The impact on wildlife and flora is unimaginable. Full support to those battling the flames.”
Deputy First Minister Michelle O’Neill voiced “huge admiration” for the firefighters and all responders.
Environment Minister Edwin Poots visited the scene on Saturday.
He described horrifying damage is being done over a widespread area, particularly to wildlife and biodiversity.
On Saturday the flames spread from Bloody Bridge, across Thomas Mountain and the base of Slieve Donard, as well up Northern Ireland’s highest peak to less accessible ground.
On Sunday the focus of firefighting efforts were in the Bloody Bridge area following overnight winds.