BOSTON — Nine people were taken to the hospital with injuries considered minor following an escalator malfunction at a Boston train station, authorities said.

The escalator from the platform up to the street-level lobby at the Back Bay Station malfunctioned at about 6 p.m. Sunday, according to a statement from the Massachusetts Bay Transportation Authority.

Boston Emergency Medical Services said in a tweet that it sent multiple ambulances to the scene and transported nine to area hospitals “with injuries reported to be minor in nature.”

Witnesses described a chaotic scene and said the escalator appeared to reverse direction and flatten out, turning into “a slide.”

The reason for the malfunction remains unclear.

“The escalator will remain out of service while the incident is thoroughly investigated,” the MBTA said.