Fire crews battling a number of forest fires burning through northwestern Ontario are finally getting a break in the weather as cooler, wetter conditions reach the region.

But officials cautioned Monday there are still major challenges to be met before the nearly 3,600 residents forced from their homes due to the threat of the fires are able to return.

Despite the change in weather over the weekend, there are still more than 100 fires burning in the area.

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More than 500,000 hectares of forest are on fire in northwestern Ontario. (Frank Gunn/Canadian Press)

The Ministry of Natural Resources warned it will either take a lot of work or a lot more rain to make a difference in the fight.

"The area that's on fire is the size of Prince Edward Island, and the forest is so dry the fires are burning underground," the CBC's Jody Porter reported Monday from Thunder Bay.

The underground blazes force firefighters to dig out the roots and other organic matter that is burning.

Many evacuees are staying in school gymnasiums, college dormitories and hotels scattered across the province as far as London and Thunder Bay.

Deputy minister of Community Safety Ian Davidson said Sunday the province was working on a plan to bring some evacuees back to their communities and reunite families who were forced to flee the fires in late June.

While some families separated during the evacuations have been reunited over the weekend, there are no immediate plans to start sending people home, the CBC's Porter said.

"We are told the evacuation centres are prepared to keep people for up to two weeks," she said.

Annie Kakepetum, a woman from Sandy Lake First Nation, was in Thunder Bay taking a course when her husband flew in with their baby in the first wave of evacuations.

Her three other children stayed behind with their grandmother to wait for another flight. They were eventually sent to Moosonee.

Kakepetum said she misses her children and talks to them on the phone as often as she can.

"They're just asking, 'When are we going to come to you, or when are we going to see you?' I couldn't answer them," she said. "Soon, I hope, I kept saying to them."

Emergency Management Ontario said it's trying to reunite families. Allison Stuart, the provincial agency's director, said teams are working on compiling a list so they can determine how many people are looking for loved ones.

"The intent is to get families together so they can support each other in a really challenging time," Stuart said.

But Stuart said reuniting families depends on the space available at evacuation centres.

Kakepetum told Porter that there's no word yet on what will happen with her family.

The communities of Cat Lake First Nation, Keewaywin First Nation, Koocheching First Nation and Sandy Lake First Nation have been fully evacuated and hosted by other communities for the time being. Another seven First Nations communities have been partially evacuated.

With files from CBC's Jody Porter