A shooting at the Washington Navy Yard threw Capitol Hill and its surrounding areas into chaos on Monday morning as law enforcement officers across the region tried to contain a security situation that involved the shooting of several people, including a police officer, and has left several dead.

Capitol Police officers headed to the scene along the Anacostia River along with Park Police, military officials, U.S. marshals, the FBI and the D.C. Metropolitan Police to locate an active shooter in the area of Navy Yard. Capitol Police also stepped up security around the Capitol as a result of the incident. As a security precaution, flights were temporarily grounded at Reagan National Airport.

Cathy Lanier, chief of the D.C. Metropolitan Police Department, on Monday afternoon said that the situation continued to evolve. She said at least one assailant was down, while as many as two others were still on the loose.

“We have one shooter we have that we believe [was] involved with this, that is deceased,” she said. “The big concern for us now is that we potentially have two other shooters that we have not located at this point.”

Patricia Ward, 53, of Woodbridge, Va., works in logistics management at the Navy Yard in Building 200.

Ward went to the cafeteria in Building 197 this morning and had just finished paying for her breakfast when she heard three gunshots.

It was “three the first time; it was quiet then for about three seconds, then pop-pop-pop-pop,” she said, adding that “everybody just started scattering out of the cafeteria and I saw some people coming out of their offices running.”

Ward said she saw a female security guard who “had her gun drawn. She said, ‘Move away as fast as you can.’ … She just told us to ‘run, run, run.’”

Ward has worked at the Navy Yard for 37 years. Asked whether she had to go through metal detectors to enter the complex, she said “no.”

Ward said she does not feel comfortable returning to work.

The shooting was reported to MPD officers at 8:26 a.m. on Monday, according to a spokesman in the public information office. A shelter-in-place situation has been ordered for parts of the Navy Yard.

President Barack Obama made remarks on the situation at a previously scheduled news conference. “I’ve been briefed by my team on the situation. We still don’t know all the facts. But we do know that several people have been shot, and some have been killed. So we are confronting yet another mass shooting. And today it happened on a military installation in our nation’s capital. It’s a shooting that targeted our military and civilian personnel. … We send our thoughts and prayers to all at the Navy Yard who’ve been touched by this tragedy. We thank them for their service. We stand with the families of those who’ve been harmed. They’re gonna need our love and support,” he said.

Kimberly Schneider, a public information officer for the Capitol Police, said in a statement that the department has several units in the area of the Navy Yard assisting MPD.

“Additionally, people may notice enhanced security operations being conducted by the USCP on the Capitol Grounds as a proactive, precautionary measure related to the active shooter incident at the Navy Yard,” Schneider said.