A Croatian firefighter has died during a deadly storm that swept the Balkans after a heatwave, bringing the death toll to six, officials have said.

Emergency services in Slovenia, Croatia, Bosnia and Serbia scrambled to restore electricity and clear the debris left over after Wednesday's chaos.

Meteorologists said the storm was extremely powerful as it was formed after a string of very hot days. Experts say extreme weather conditions are likely fueled by climate change.

Elsewhere in Europe, a continuing heatwave caused wildfires and public health warnings.

Throughout the Balkan region, authorities reported hundreds of people injured, including around 20 seriously, from fallen trees, roof parts or other objects blown off by the swirling winds.

The firefighter in the eastern Croatian town of Tovarnik died “tragically” during the storm, his unit said, revealing no other details.

“It comes swiftly"

Three more people died on Wednesday in Croatia, one in Slovenia and one in Bosnia. Serbia's police said emergency crews saved 40 people and put out 20 fires caused by lightning.

“Four dead people from a storm like this is a terrible, huge tragedy,” said Croatian Prime Minister Andrej Plenkovic as he visited a park in the capital, Zagreb, where more than 200 trees were blown down.

Plenkovic said Croatia will establish a warning system for natural disasters and other dangers like Wednesday's storm.

“There are not too many ways to counter this type of storm,” Plenkovic added. “It comes swiftly, it is powerful and it then moves on.”

Tens of thousands of people were also left without electricity in Slovenia, Croatia and Serbia.

Emergency measures are usually declared for floods or similar natural disasters to enable local authorities to draw more funds and people during a crisis situation.

Authorities have warned that more storms are possible in the next few days before the next wave of very hot weather begins.