ROME — The authorities in Italy on Wednesday were investigating why a subway escalator in Rome suddenly sped up during rush hour and raced to the bottom, dumping riders in a crush of bodies and leaving dozens hurt, including one man with a seriously injured foot.

Footage on social media showed passengers screaming as the stairway appeared to crumple after racing down the Repubblica station in central Rome on Tuesday evening. A video showed a man on a parallel escalator dragging one person to safety, while others jumped on the dividing barrier or tried to help those trapped at the bottom.

More than 20 people were hurt, according to news reports. Some of the injuries resulted because the shattered stairs acted like sharp blades on the feet, heels, ankles and lower legs of the passengers, rescue workers said.