An aerial view of the fire in Ljusdal. Photo: Maja Suslin/TT

As Sweden battles dozens of wildfires across the country, the Civil Contingencies Agency (MSB) warned on Friday that it is currently "impossible" to extinguish some of the largest blazes.

Instead, authorities expect it could take up to several months before the fires stop smouldering.

"Four of the fires are now judged to have a serious character; they've grown to such a size that it's not possible to put them out at the moment," Marcus Årskog, the spokesperson for MSB's wildfire group, told the TT newswire.

"What we can do is work to limit them so that they don't spread towards villages or inhabited areas," he added.

The serious blazes in question are all located in central Sweden: Fågelsjö/Lillåsen in Jämtland, Kårböle in Gävleborg, Trängslet in Dalarna and Brattsjö in Västernorrland.

MSB's head, Dan Eliasson, has said Sweden's emergency services are facing the most serious situation they've ever experienced.

In total, between 300 and 500 people have been forced to evacuate their homes, according to MSB's information, while emergency services operator SOS Alarm said on Friday afternoon that there were currently 61 fires burning across the country.