Commuters on a rush-hour train were sent running for the exits in a panic after a subway hit an object on the tracks and caused the 59th Street and Lexington station to fill with smoke on Monday evening.

The frantic scene unfolded just after 6 p.m. as a northbound 6 trail struck the unidentified object as it pulled into the station, the MTA and FDNY said.

When the train doors opened a “mad rush of people” filed out and fled out of the station, straphanger Frazer Rice told The Post.

“People were definitely sprinting to the left and then two cops walked by, looked inside at the people confused in the subway car and said ‘Get out now.’ And we got out and everyone else was sort of running and that was about it,” recalled Rice, who was heading uptown from Spring Street.

It wasn’t immediately clear what the train struck. No injuries were reported.

The NYPD confirmed that officers were on scene to help evacuate commuters from the smoke.

Rice, who said he did not see any smoke himself, said he believed the panic started when other riders saw people sprinting and decided they should too.

“Until the doors opened, I think people saw people start moving to rush to the left but there wasn’t anything to elicit panic. But when the doors opened it was pretty clear people were running and then people got out.”

“The two cops who were there were on the scene very quickly,” he added. “The doors opened and it couldn’t have been more than 5 or 10 second that they were on the way to the rear of the platform and saying ‘alright, everybody get out.’”

The incident impacted service along the 4-5-6 lines, however, which were running with delays by 6:45 p.m., the MTA said in a tweet.