Lightning struck 11 people, including eight children, who had gathered in a Paris for a child’s birthday party Saturday, officials said.

Among those hit in Park Monceau, four children and two adults were seriously injured, said Paris fire service spokesman Eric Moulin, the Associated Press reported.

Four of those seriously injured are in life-threatening condition, Moulin said. One adult and five children were slightly injured, he said.

“They had taken shelter under a tree,” Paris city councilor Karen Taieb told Agence France-Presse.

An off-duty fireman near the park, a popular weekend spot for Paris’s well-to-do, ran to the scene and saw nine people lying on the ground under a tree, Moulin told AP.

The off-duty fireman delivered first aid to victims; “without his actions, it would have been much worse,” Moulin said.

The victims had burns, Vincent Baladi, an official in Paris’s eighth district, said on iTELE television.

“We hope they will all pull through,” he told the station, according to AFP. “The lightning struck suddenly.”

France’s families minister, Laurence Rossignol, tweeted, “all my thoughts are with the children” injured and their families.

On Friday, the country’s meteorological service warned about the possibility of thunderstorms throughout the weekend.