The previous record was set in 1972 when a heatwave lasted 14 days. The extreme heat is expected to last until early next week.
The highest temperature of the heatwave, 31.7C, was recorded at two locations, Ylitornio and Sodankylä, earlier this week.
However, the hot weather has led to renewed concern over the fast pace of climate change in the Arctic, which is warming up to five times faster than the global average, according to the UN’s intergovernmental panel on climate change.
“Due to climate change, these sorts of heatwaves in Lapland are expected to become longer and more intensive over this century,” said Siiskonen.
Emergency services have also been dealing with several dozen fast-spreading wildfires in the wilderness further north of Rovaniemi this week.
Because of the size and remoteness of Lapland, fires often burn for long stretches of time before firefighters are able to arrive on the scene. Finnish authorities have warned the population the risk of wildfires remains high.
In Rovaniemi, schools and nurseries have cancelled some outdoor activities, authorities have told residents to check on their elderly neighbours and health officials are warning people of the need to stay hydrated.
Despite the limited chaos, Sanna Kärkkäinen, managing director of Visit Rovaniemi, said the heat had not affected the city’s most popular tourist destination.
“The weather has certainly surprised locals and tourists,” she told the Telegraph, but the Santa Claus Village, where visitors can meet the man himself, “remains open seven days a week”.
Lapland’s reindeer, with their thick coats, are suffering in the heat and are also being attacked by mosquitoes. The animals, which mostly roam freely, have been trying to move to higher ground or travel into villages or to the beach in search of relief.
Toivo Koivu, a resident of Rovaniemi who has just finished travelling through southern Europe, said he was shocked to return to such heat.
“We thought that when we would come back to Finland it would be cooler, like normally – but no, it was the same weather as down south,” he told Reuters.
It comes as other parts of Europe have been gripped by heatwaves and wildfires this summer.
June was the hottest on record globally, and authorities in Spain, Portugal, Greece and France were forced to issue extreme heat warnings as temperatures went above 42C.