In southern Poland, a man in his 40s was killed when he was struck by lightning as he descended the Babia Gora mountain, according to reports.

In Germany, a total of 33 people, including 29 youngsters aged nine to 11, were treated after a bolt hit a pitch where a junior soccer game was being played, in the western town of Hoppstädten.

The 45-year-old referee suffered a direct strike and was taken to hospital by helicopter. He was one of three adults seriously injured.

The game had just finished when the lightning hit at about 2pm on Saturday, according to a police spokesman.

He told German TV: "According to what everyone present says, there were no clouds in the sky... so that this incident couldn't have been expected."

Parts of western Germany have seen storms, heavy rain and hail over the past two days.

Children's birthday party

The incident came on the same day as a lightning strike at a children's birthday party in a Parisian park left 11 people in hospital, including at least two in a life-threatening condition.

The victims were at Parc Monceau in the northwest of the city when the thunderstorm struck.

They had tried to take shelter under a tree, but were hit by lightning.

Professeur Pierre Carli, director of Hospital Necker in Paris, said three adults - one woman and two men - were in hospital, along with eight children - one of them on life support.

The children are believed to be aged between seven and 14.

Police were quick to set up a medical unit on site to treat some of the victims, with others rushed to hospital.

Fire service spokesperson Eric Moulin said an off-duty fire officer ran to the scene after the lightning struck, administering first aid, including heart massages, and helping direct rescuers to the area.

"Without his help in those initial moments, the situation would have been much worse," Mr Moulin said, adding that it was a timely reminder of the need to know first aid.