Paris (CNN) A massive fire ripped through a Parisian apartment building Wednesday morning, killing at least eight people -- including two children, officials said.

The cause of the fire has not been determined. Police are investigating whether the fire was set.

The fire broke out on the ground floor around 4:30 a.m. and spread to the stairwell, Paris Mayor Anne Hidalgo said in a statement. She said more than 100 firefighters battled the blaze for three hours.

By late Wednesday morning, the fire was under control, the mayor said.

"On behalf of the Paris citizens and myself, I would like to give my sincere condolences to the families and relatives of the victims," Hidalgo said. "I want to tell them that, this morning, Paris is mourning."