Meteorologists across the Nordic countries have registered near-record temperatures over the weekend, including highs of 34C in some places, news agencies reported.
The latest figures came after Finland's national meteorological institute registered its hottest temperature for June since records began in 1844.
Kevo in Lapland, at the far north of Finland, recorded heat of 33.5C on Sunday, the hottest since 1914 when authorities registered 34.7C, said the STT agency.
Several parts of Sweden also reported record highs for last month.
"June 2021 was the hottest June ever recorded in my hometown Stockholm by a large margin," climate campaigner Greta Thunberg tweeted.
"The second hottest June was in 2020. The third in 2019," she added.
"Am I sensing a pattern here? Nah, probably just another coincidence."
At a national level, June 2021 was the third-hottest ever recorded in Sweden.
Norway's meteorological institute registered 34C in Saltdal, a county near the Polar Circle.
That is the highest temperature measured in the country this year, and just 1.6C short of Norway's all-time record.
Several parts of the world have already experienced crushing heatwaves this year.
Canada is battling a string of forest fires in the western province of British Columbia after sweltering under temperatures of up to 49.6C, a new national record.
On Thursday, the United Nations confirmed a new record high temperature for the Antarctic continent, measured last year, of 18.3C.