At least five people, including two children, have died and more than 100 have been injured during a sudden thunderstorm in Poland and Slovakia’s Tatra mountains, according to rescuers.

Most of the victims were in Poland, where lightning struck a metal cross atop Mount Giewont as well as a metal chain near the summit, according to local media. The four dead in Poland included two children, a spokeswoman for the Polish air ambulance service, Kinga Czerwinska, told the news broadcaster TVN24. One person died in Slovakia.

“There were a few deaths in different parts of the Tatra mountains,” said Jan Krzysztof, a Polish mountain rescue service chief told Poland’s PAP news agency.

“More than 100 people are injured,” Poland’s prime minister, Mateusz Morawiecki, said after arriving in the nearby mountain resort town of Zakopane. He said some were in a very serious condition, suffering from burns or head injuries.

Rescuers believe many hikers were present when lightning struck the cross on Giewont’s summit. They had set out to climb Poland’s highest mountains when the skies were clear earlier in the day.

“We heard that after [the] lightning struck, people fell … The current then continued along the chains securing the ascent, striking everyone along the way. It looked bad,” Krzysztof said.

Lightning also struck on the nearby Czerwone Wierchy mountain massif, injuring a Portuguese citizen.

It was also announced on Thursday that Polish rescuers had found the body of one of two cavers trapped in a cavern in the mountains since Saturday. “The first of the cavers has been found in the cave, he is dead. More information will be available tomorrow,” , said the local mountain rescue service, TOPR.

The two became trapped in the Wielka Śnieżna cave, the longest and deepest in the Tatra mountains, on Saturday, and rescue services were notified by colleagues who had accompanied them on the excursion.

Agence France Presse, Associated Press and Reuters contributed to this report