The Swedish Civil Contingencies Agency (MSB) said two Italian firefighting aircraft had been sent to assist in badly hit areas of central Sweden, while Norway had dispatched six helicopters.
Swedish authorities said 44 fires were burning across the country on Wednesday, urging locals living close to the blazes in the central counties of Gavleborg, Jamtland and Dalarna to evacuate.
Even northern Swedish Lapland, inside the Arctic Circle, has been affected.
Five wildfires were burning Wednesday in the forests outside the town of Jokkmokk, a popular tourist destination in the winter.
“The last time we saw wildfires of this calibre was 12 years ago,” Jokkmokk rescue officer Thomas Andersson told AFP.
MSB fire chief Britta Ramberg told TT news agency the fire in Jamtland was “the largest and spreading the fastest”.
The fire there had already engulfed 2,500 hectares (6,000 acres) and was spreading by 10 square metres (100 square feet) a minute, authorities said.
No casualties have been reported so far.
MSB said it had asked the EU Civil Protection Mechanism for more firefighting planes in addition to those sent from Italy due to lack of capacity and manpower.
“The drought has led to a large amount of simultaneous fires in the forests and land,” emergency services company SOS Alarm said in a statement, adding that the number of fires would “likely” increase on Wednesday.
“This is not looking good, it’s burning uncontrollably and spreading quickly,” rescue officer Torbjorn Wannqvist told TT.
Meteorologists have in recent days warned of extremely hot temperatures in Sweden, saying it’s “unusual” for a heatwave to last this long.
Record temperatures above 33 degrees Celsius (90 degrees Fahrenheit) were reported in Uppsala, a city north of Stockholm, and more than 30 degrees throughout the rest of the country.
Neighbouring Norway was hit by wildfires in 100 locations in the south last week, some of which were triggered by lightning.