Paris, 18 January 2025 (dpa/MIA) — It's probably a birthday they'll never forget.

A woman was celebrating her 60th birthday with around 50 guests on the fifth floor of her Paris apartment building shortly before midnight on Saturday when the floor suddenly collapsed, sending partygoers crashing into the fourth-floor flat below.

Twenty people were injured, one seriously, a spokesman for the fire brigade said on Sunday.

"It was a birthday party, and then, when we were about to cut the birthday cake, the floor suddenly gave way, a guest told the broadcaster RTL.

"We felt nothing and suddenly found ourselves on the floor below."

He said he was with his brother at the end of the living room and first saw guests in the middle of the room fall to the floor before the rest of the living room also collapsed.

"We inevitably found ourselves with people under us, above us and next to us."

Authorities said the building's structure was not damaged by the floor's collapse.

"The floor was vibrating, probably because several people jumped at the same time, which made the floor unstable and it collapsed," the Paris prefecture's security architect, Antoine Cardon, told RTL.