CHICAGO (WLS) — Two men were shot and killed at Navy Pier Tuesday afternoon, Chicago fire officials said.

Chicago police and fire crews responded around 1:30 p.m. to a report of shots fired at an administrative office near a loading dock in the 600 block of East Grand Avenue, police said at a news conference Tuesday .

ABC7 Chicago is now on the air 24/7. Click here to watch

A male Levy employee who had been fired a month earlier fired the shots, police said.

“As the subcontractor’s former employer, he had access. He knew how to get to that rear loading dock area,” said Brian Murphy, director of operations at Navy Pier.

A 47-year-old man and a 51-year-old man, the employee’s former colleagues, were shot in the head, police said. They were taken to Northwestern Memorial Hospital in critical condition. They later died, police said.

SEE ALSO: Chicago police officer killed in East Chatham, shot with ID; 2 in custody

Their identities were not immediately released.

Navy Pier was closed for nearly an hour, but officials said the incident happened at the popular tourist destination in the middle of the isolated afternoon.

“We had to shut down the whole store, shut down the whole Navy Pier. Everyone was just closing. We had customers coming in the back,” Navy Pier worker Diamond Foster said.

Police have identified a person of interest, who is at large.

A shelter in place at Navy Pier was lifted after police determined via security cameras that the shooter had left the area.

“They’re talking about, ‘Okay, everybody keep calm, but it’s a minor threat,'” said Navy Pier visitor William Wright. “Everyone really starts out as a minor threat. This should be Navy Pier.”

Police have not said who they are looking for, only that the shooter was a former employee of a Navy Pier subcontractor.

There was a large Chicago Police response on the north side of the pier near the parking lot. CPD officers in tactical gear were seen in the area around 2 p.m

“We took out the automatic weapons, full SWAT gear, shields, the works,” Ohio resident Trent Halasek said.

Area detectives are investigating.

No weapon was recovered and police remained at the scene around 5 p.m.

Levy issued a statement, saying: “We are absolutely devastated by today’s tragic events and the shocking loss of two members of our family. Our hearts break for their families and loved ones, whose lives are changed forever.”

INTERACTIVE SECURITY TRACKER | Track crime and safety in your neighborhood