At least one person was shot in Midtown Manhattan on Monday evening, and the office building that houses the offices of the investment giant Blackstone was locked down as the police sought the gunman, according to a witness at the scene.

The police did not immediately provide details of the shooting, including the condition of the wounded person.

The shooting occurred about 6 p.m. in the area of the Blackstone building, at 345 Park Avenue, between 51st Street and 52nd Street. By 6:10 p.m., dozens of officers had flooded the area, according to the witness, Ben Ryder Howe, a freelance journalist. By about 7 p.m., people began to march out of the building in small groups with their hands raised, he said.

This is a developing story and will be updated.