A New York City subway train derailed Thursday after colliding with another train at low speed, leaving more than 20 people with minor injuries and causing major service disruptions across Manhattan during the afternoon rush hour, authorities said.

At about 3 p.m. on the Upper West Side, a 1 train carrying about 300 passengers and an out-of-service Metropolitan Transportation Authority train with four workers on board hit each other near the 96th Street station, police and transit officials said at the scene. A “derailment” is when at least one wheel of a train leaves the track.

Photos posted on social media by city emergency management officials showed the passenger train partially off the tracks in an area that had a track-switching mechanism. Officials said there were no immediate signs of equipment failure and investigators were seeing if human error was involved.