Five people have been killed by lightning strikes across mountains in southern Poland and Slovakia, including one man who fell down the side of a mountain after being struck.

Key points: More than 100 people were injured in the thunderstorm across the Tatra mountains

More than 100 people were injured in the thunderstorm across the Tatra mountains Two children were among those killed, and authorities believe the death toll could rise

Two children were among those killed, and authorities believe the death toll could rise Polish rescuers believe lightning may have struck metal chains installed to aid tourists in their climb

Authorities said more than 100 people were injured in the thunderstorm on Thursday, which hit the Tatra mountains, an area popular with hikers and families.

Witnesses said the thunderstorm came suddenly on a day that began with clear weather.

The lightning strikes pummelled Poland's Giewont peak, a trekking destination that is 1,894 metres high, as well as other locations across the Tatras.

The Slovak rescue service said a Czech man was killed after lightning knocked him off Banikov peak.

The tourist fell hundreds of metres down the side of a mountain.

Four people were killed on the Polish side, including two children, a spokeswoman for the Polish air ambulance service, Kinga Czerwinska, told the news broadcaster TVN24.

A Czech tourist fell hundreds of metres down the side of the Banikov Mountain after being struck by lightning. ( Miroslav Blaho/Wikimedia Commons, File )

Rescuers with the Polish Tatra emergency service, known as TOPR, said they believe the lightning may have hit some of the metal chains installed on Giewont peak to aid tourists in their climb.

Some of the injured were taken by helicopter to a hospital in the Polish mountain resort of Zakopane.

Krakow Governor Piotr Cwik told reporters that the death toll could rise.

Prime Minister Mateusz Morawiecki said some of those injured were in a serious condition with severe burns or head injuries, as they fell after the lightning strikes or were hit by falling rocks.

He extended his sympathies to their relatives.

The Tatras, part of the Carpathian mountain range, are the highest mountains in Poland and Slovakia and attract tourists from near and far with scenic lakes and peaks that soar up to 2,655 metres.

Many of the injured are in a serious condition with severe burns or head injuries. ( AP: Bartlomiej Jurecki )

'You could hear thunder from every possible direction'

Tourist Grzegorz Pyzel told TVN24 he was halfway up Giewont peak with his wife in clear weather when suddenly they heard thunder and thought it was a jet overhead.

"But soon lightning struck and we turned back. Suddenly it started pouring and you could hear thunder roaring from every possible direction," Mr Pyzel said.

The couple reached a shelter on Hala Kondratowa, at the foot of the mountain. He said others started coming in, saying there were injured people further up the mountain.

Footage on TVN24 showed rescuers racing to a helicopter to get to the peak in rainy, foggy weather and then a helicopter landing at the hospital in Zakopane with injured people.

Rescue workers planned to keep checking the mountains for anyone else who might need help.

Thursday's lightning strikes were the worst accident in the Tatras since August 1937, when lighting killed four people on Giewont.

In another rescue operation in the Tatra mountains, TOPR emergency workers have been searching for two spelunkers who went missing in a cave on Saturday after being trapped by rising water.

Rescuers used small amounts of explosives to widen passages in uncharted parts of the Wielka Sniezna cave, Poland's deepest and longest, to look for the missing cavers.

On Thursday, the body of one of the two was found, an official said.

AP