At least four people are dead and four missing after a building collapsed in Marseille, France, Sunday.

Rescue operations continued Monday morning to find the four people who are missing.

What caused the Marseille building to collapse?

An explosion early Sunday morning caused the apartment building to collapse. but the exact cause of the explosion is still under investigation, The Associated Press reported.

A gas leak is one possible cause that is being explored, with local residents noting that they smelled gas following the explosion, according to BBC News.

How many people died in the Marseille building collapse?

As of Monday morning, four bodies had been recovered from the rubble. Four more people are still missing.

“The hope to find survivors is still there,” Minister for Cities and Housing Olivier Klein said, per AP. “It is very meticulous work done by firefighters.”

How did Macron react to the Marseille building collapse?

French President Emmanuel Macron expressed his sympathies to those affected in a tweet Sunday: “Thoughts with Marseille, where a building on rue Tivoli collapsed last night. I am thinking of those affected and their loved ones. An investigation is continuing with significant resources deployed. Thank you to the firefighters and rescuers mobilized,” he said, according to CNN.