As the sun rose in Paris, investigators have begun their probe into what caused the blaze at Notre Dame cathedral and questioned workers on the building, according to a report.

By dawn on Tuesday, the cathedral stood in the sunlight with no signs of smoke emanating from its walls. French authorities said the fire was under control early Tuesday morning, but parts of its roof continued to smolder, the New York Times reported.

Also on Tuesday morning, the Paris Prosecutor’s office began speaking with the construction workers who were working on the site when the flames erupted, CNN reported.

Despite the questioning of the workers, an official cause of the blaze has still not been announced.

On Monday night, French President Emmanuel Macron vowed to rebuild the damaged parts of the building.

“We will rebuild Notre-Dame,” he said near the Cathedral’s grounds on Monday night. “Because that is what the French expect.”

On Monday afternoon, the iconic cathedral went up in flames, toppling over its spire and sending plumes of smoke into the Paris sky.