Most of the victims were on the Polish side of the border, where a flash struck a group of about ten tourists on the mountain of Giewont. At the top of the nearly 1,900 meter high mountain stands a 15 meter high iron cross which the flash is suspected to have struck.

"No one expected such a sudden storm to break out and from a human perspective it was something that was impossible to predict," said Poland's Prime Minister Mateusz Morawiecki, who traveled to a crisis meeting in the nearby town of Zakopane.

At least two of the victims were children and three injured persons received intensive care.

Over 100 people injured

In a western Slovak part of the mountain range, a man fell into a ravine in connection with a lightning strike.

Another over 100 people have been injured in various ways in different parts of the mountainous area, according to the Polish Prime Minister. Zakopane authorities have announced a mourning day on Friday, reports the Polish news agency PAP.

A rescue operation is already underway in the Tatra Mountains, when two climbers were trapped in a cave when it was flooded last Sunday. About 20 rescue workers participate in this effort.