A Capitol police officer shot and injured a man who brought a weapon into the U.S. Capitol Visitor Center Monday afternoon, the chief of Capitol Police said.

An officer fired after the man pointed what appeared to be a weapon at him, U.S. Capitol Police Chief Matthew Verderosa said. The man was wounded and was in surgery Monday afternoon at Washington Hospital Center, where he is listed in critical condition, according to hospital officials.

The U.S. Capitol Police Department said Larry R. Dawson, 66, of Antioch, Tennessee, has been charged with assault with a deadly weapon and assault on a police officer while armed. They said Dawson's vehicle was located near the Capitol and was secured at a separate location.

A female bystander received minor injuries and also was taken to a hospital.

"We believe that this is the act of a single person who has frequented the Capitol grounds before, and there is no reason to believe this is anything more than a criminal act," Verderosa said at a news conference.

The man went through a metal detector at the visitor center, an alarm went off and he pulled out the gun, two sources told News4's Shomari Stone.

"It appears the screening process worked as intended," Verderosa said, noting the suspect has not yet been charged. A weapon was recovered at the scene.

NBC News’ Pete Williams reported early Monday evening that the weapon was a pellet gun. Dawson was known to U.S. Capitol Police and was a frequent visitor, Williams reported.

Dawson is facing charges for allegedly standing up and shouting Bible verses in October 2015 in the House Chamber Gallery. According to court documents from the Superior Court for the District of Columbia, Dawson identified himself as a “Prophet of God” to the people in the gallery.

According to the documents, Dawson was removed from gallery and, while being removed from the building, pushed a police officer and began to run. He was caught and charged with assault on a police officer.

A Stay Away Order was issued to Dawson, including a map of the area he was supposed to avoid, which included the U.S. Capitol building and grounds, including all Congressional buildings.

The U.S. Capitol complex was locked down about 3 p.m. The shelter-in-place order was lifted at 3:45 p.m., but the Capitol was open only for official business. The visitor center remained closed.

At first, anyone outside was advised to seek cover immediately, U.S. Capitol police said. The D.C. Police Department later said in an update that there had been an isolated incident and there was no threat to the public.

Visitors were turned away from the Capitol as emergency vehicles flooded the street and the plaza on the building's eastern side. Police, some carrying long guns, cordoned off the streets immediately around the building, which were thick with tourists visiting for spring holidays and the Cherry Blossom Festival.

Initial reports by The Associated Press said a police officer sustained minor injuries. Sources told Williams and Stone that was not the case. Verderosa said no officers were injured.

The visitor center will be open as usual on Tuesday, Verderosa said.

Jill Epstein, executive director of the California Association of Marriage and Family Therapists, told NBC News she was at the visitor center on a lobbying trip to meet a senator when an active shooter was reported.

There has been an isolated incident at the US Capitol. There is no active threat to the public — DC Police Department (@DCPoliceDept) March 28, 2016

Due to police activity, Capitol Police have issued a shelter in place for the Capitol complex. Please stay in your designated area. #alert — SenateSergeantAtArms (@SenateSAA) March 28, 2016

"I was with a group of my colleagues walking into the visitor center and as we were literally going through the metal detectors, people started screaming, 'Get out! Get out!' We didn't know which way to run. We ran out and and they told us to get against the wall so we were crouching against the wall outside the visitor center,” she said.

"Police appeared out of everywhere and they were screaming, 'Run for it! Run for it! Run up that ramp!' And we ran like you see in videos. It was surreal. It was so beautiful out and the cherry blossoms are in bloom and people are running for their lives. It was unsettling and scary," Epstein said.

No is getting in here barricading in #USCongress #Washington_DC A photo posted by Mouaz Moustafa (@soccermouaz) on Mar 28, 2016 at 12:25pm PDT

The witness said one of her colleagues bolted for the door without his watch, wallet or phone, which were still on the conveyor belt of the metal detector.

It's the second time in less than a year that the U.S. Capitol was locked down due to a gun incident. Last April, a 22-year-old from Lincolnwood, Illinois, fatally shot himself on the building’s west front, triggering an hourslong lockdown.

A dental hygienist from Connecticut, Miriam Carey, 34, was shot and killed outside the Capitol Oct. 3, 2013, after police said she tried to ram a temporary security barrier outside the White House with her car and then struck a Secret Service uniformed division officer. She then fled the scene, leading police on a chase.

According to subsequent investigation by the News4 I-team, U.S. Capitol police stopped at least 13 people from carrying guns on or near Capitol grounds from 2012 to 2015.

On July 24, 1998, two U.S. Capitol Police officers were killed after a gunman stormed past a Capitol security checkpoint and opened fire. Officer Jacob J. Chestnut Jr. was fatally shot at the checkpoint, and a tourist was injured in the initial crossfire between the gunman and police. Detective John M. Gibson then told congressional aides to seek cover before exchanging gunfire with the shooter. Gibson was fatally wounded, but police say his actions allowed other officers to subdue the gunman.