Two brothers have been killed by a lightning strike in eastern Finland while they were heating up a sauna at their summer cottage, according to local police.

The two men, both in their 60s, were staying with their sister in Juuka, a community of 3,200 in the Northern Karelia region of Finland.

They had gone out to heat the sauna late on Friday when a loud bang was heard.

Upon hearing the sound, the woman ran out of the cottage to find her brothers on the ground.

A nearby spruce tree was also damaged, leading police to suspect that lightning struck the tree and then its powerful electric charge was conducted into the men's bodies by the wet soil.

Finland was hit by a massive onslaught of thunderstorms beginning on Thursday, driving away the hot, dry weather that had spread across the country.

According to Finnish news outlet Yle, the Finnish Meteorological Institute (FMI) reported 20,000 lightning bolts striking the country, setting a new record for this summer.

Timelapse footage of the change in weather over London

FMI has issued warnings in recent days for everything from thunderstorms and heavy rain to severe heat and forest fire risk as the extreme weather blanketing Europe takes its toll on the northern nation.

More electrical storms are expected over the weekend.

While the incident in Juuka was shocking, the Finnish Medical Society Duodecim said lightning tends to kill just one or two people each year in Finland.

Around the same number of lightning related deaths occur in the UK, with one study reporting that in the 30-year period ending in 2016, 58 people had reportedly died in this manner.

The highest proportion of lightning-related deaths occurs in young men, a figure experts think might reflect engagement in outdoor work and pursuits that put people at risk of lightning strike.

Moisture increases the conductivity of electrical current so a wet location is more likely to result in a fatal strike than a dry one.

Anyone caught in a thunderstorm should seek refuge in a building of vehicle, or if that is impossible simply crouch down and remain low until the threat has passed.

In July a woman from Galashiels in Scotland reported being struck by lightning while she tried to film a thunderstorm out of her window. Tracey Kutluol warned others: “Don't be a numpty like me”.