U.S. Representative Pramila Jayapal said she has tested positive for COVID-19 after being locked in a room with Republican lawmakers who refused to wear masks as President Donald Trump's supporters laid siege to the U.S Capitol.

A Democrat, Jayapal, 55, lambasted Republicans late on Monday and said many of them not only refused to wear a mask while stuck in the room for several hours but also mocked colleagues and staff when offered one.

"Too many Republicans have refused to take this pandemic and virus seriously, and in doing so, they endanger everyone around them," she said in a statement.

Jayapal, who is the second Democratic member of the U.S. Congress to test positive since last Wednesday's storming of the Capitol by Trump's supporters, said she would work in isolation, in line with the guidance of the Capitol physician.

The attending physician for Congress, Dr Brian Monahan, said lawmakers who hid together for hours in a closed room to avoid the mob may have been exposed to the coronavirus.

Health officials have warned that the attack would likely become a superspreader event, as lawmakers were isolated for hours while a violent crowd of mostly maskless Trump supporters roamed the halls and corridors in an unsuccessful bid to block lawmakers' certification of Joe Biden's presidential win.