WASHINGTON, Jan. 6 (Xinhua) -- The U.S. Capitol was breached by protesters on Wednesday afternoon, a tense situation that has forced proceedings to count Electoral College votes cast in the 2020 presidential election to halt.

Lawmakers are reportedly being evacuated from the House and the Senate, as protesters supporting outgoing President Donald Trump, a Republican, forced their way into the building, which has been placed under a lockdown, and entered the chambers.

"All buildings within the Capitol Complex, Capitol: External security threat, no entry or exit is permitted, stay away from exterior windows, doors. If outside, seek cover," according to a message from Capitol Police.

U.S. Congresswoman Nancy Mace of South Carolina, tweeted out a video clip showing physical confrontation between protesters and police.

"Just evacuated my office in Cannon due to a nearby threat. Now we're seeing protesters assaulting Capitol Police," she wrote. "This is wrong... I'm heartbroken for our nation today."

A woman is reportedly in critical condition after being shot in the chest on the Capitol grounds.

At least five people, including a law enforcement officer, have been transported to the hospital, according to D.C. emergency authorities. Several officers have been treated for pepper spray exposure.

Trump tweeted he's asking "everyone at the U.S. Capitol to remain peaceful."

"No violence," he wrote. "Respect the Law and our great men and women in Blue. Thank you!"

Vice President Mike Pence, who was presiding the congressional session certifying President-elect and Democrat Joe Biden's victory over Trump, issued a much stronger statement.

"The violence and destruction taking place at the US Capitol Must Stop and it Must Stop Now," Pence tweeted. "Anyone involved must respect Law Enforcement officers and immediately leave the building."

In a joint statement, House Speaker Nancy Pelosi and Senate Minority Leader Chuck Schumer, top congressional Democrats, said that they are "calling on President Trump to demand that all protestors leave the U.S. Capitol and Capitol Grounds immediately."

The entire D.C. National Guard has been activated following breach of the U.S. Capitol, according to Jonathan Hoffman, chief spokesman for the Pentagon. Virginia is also sending 200 state troopers and mobilizing a unit of the Guard to respond to the situation, a state official said.

D.C. Mayor Muriel Bowser on Wednesday afternoon ordered a citywide curfew in the wake of the incidents.

In a statement, Bowser said the curfew will run from 6 p.m. on Wednesday until 6 a.m. on Thursday.

"During the hours of the curfew, no person, other than persons designated by the Mayor, shall walk, bike, run, loiter, stand, or motor by car or other mode of transport upon any street, alley, park, or other public place within the District," Bowser said.