A massive fire under a bridge spanning the Ohio River closed a busy highway between Cincinnati and northern Kentucky on Friday and damaged part of the steel structure. No injuries were reported.

The fire broke out overnight near a playground under the bridge, closing Interstate 471, according to the Cincinnati Fire Department.

Video showed flames rising more than 40 feet into the air and igniting a short section of the bridge, known for its yellow arches, near downtown Cincinnati. Pieces of concrete fell from the bridge and the fire deformed some of its steel beams, firefighters reported.

The most extensive damage was on the bridge’s southbound lanes leading into Kentucky and will take weeks to repair, said Matt Bruning, a spokesman for the Ohio Department of Transportation.

At least three beams and a section of the roadway will need to be replaced, he said.

The cause of the fire remains under investigation, said Frank McKinley, the city’s fire chief. The flames were fueled by mulch as well as plastic and wooden play structures located under the bridge, he said.

More than 60 firefighters helped bring the blaze under control, he said.