Finland, Norway and Sweden experienced unusually hot weather for two weeks in the second half of July as temperatures soared above 30C, with Finland seeing 22 consecutive days of temperatures above 30C.

The persistent heat led to people fainting at outdoor events, overcrowded and overheated hospitals, wildfires, algae blooms, a surge in drownings, and sightings of reindeer seeking shade in towns, the two dozen European researchers said in a report published by the World Weather Attribution.

"Climate change made the heatwave about 2C hotter and at least 10 times more likely," their rapid analysis showed.

The heatwave was intensified by the burning of fossil fuels, which release planet-heating carbon emissions, they said.

"Climate change is fundamentally reshaping the world we live in," Clair Barnes, a researcher at the Centre for Environmental Policy at Imperial College London said in a statement.

"Cold-climate countries like Norway, Sweden and Finland are now experiencing unfamiliar levels of heat, as recently seen in strained health systems and sightings of reindeer seeking shade in urban areas," she said.

The report came as temperatures were again expected to soar to almost 30C in parts of the region on Thursday.

The Nordic countries are known for their cooler climate and are not normally considered vulnerable to high temperatures.

"Our infrastructure was not built to withstand these extreme temperatures and our ageing population is increasingly susceptible to dangerous heat," Maja Vahlberg, a climate consultant at the Swedish Red Cross said in the report.

Buildings in the region are often well-insulated but poorly ventilated, Vahlberg told reporters at a press briefing.

The researchers also noted that warmer temperatures were threatening the livelihood of indigenous Sami reindeer herders in the north.

Reindeer normally move to higher ground in summer but those areas now offer less relief, causing the animals to overheat and struggle to find food and water.

Additionally, warmer winters cause more snow to fall as rain, with alternating periods of freeze and thaw building layers of ice that prevent reindeer from digging for food.

The Arctic region is heating far faster than other parts of the planet, other studies have shown.

Barnes said that the likelihood of a prolonged period of heat like the recent heatwave has almost doubled since 2018, when the region last experienced such an intense heatwave.

"A rapid transition from fossil fuels to renewable energy is the only way to slow and, hopefully, ultimately stop this warming," she said.