ATLANTA — A massive fire caused an interstate bridge to collapse during rush hour Thursday in Atlanta, just minutes after witnesses said police halted traffic and turned cars away from the crumbling overpass. However, officials said no one was hurt despite dramatic images of towering flames and plumes of smoke.

The fire burned for more than an hour under I-85 northbound near Piedmont Road, spewing large clouds of black smoke skyward. The interstate — a major artery for the U.S. South that runs through the heart of Atlanta — was closed indefinitely.

The impact on traffic long-term was not immediately known, but traffic was bumper to bumper on nearby surface streets Thursday night as people scrambled to find alternate routes.

“This is about as serious a transportation crisis as we can imagine,” Mayor Kasim Reed said.