A heat wave that has embroiled Europe all week could cause the fire-damaged parts of Notre Dame to collapse, according to Chief Architect Philippe Villeneuve.

"I am very worried about the heat wave because, as you know, the Cathedral suffered from the fire, the beams coming down, but also the shock from the water from the firefighters. The masonry is saturated with water," Villeneuve told Reuters on Wednesday.

The wood roof and spire of the 850-year-old cathedral in Paris was consumed by fire on April 15. Since then, some damaged areas of have not been accessible or restored.

"What I fear is that the joints or the masonry, as they dry, lose their coherence, their cohesion and their structural qualities and that all of sudden, the vault gives way," he said.

Temperatures in Paris hit a record 42 degrees C (107.6 Fahrenheit) on Thursday. The scorcher was followed by a little rain and thunder in the evening, with lesser heat expected over the weekend.