House Speaker Nancy Pelosi said lawmakers will resume counting electoral votes Wednesday once the US Capitol is given an all clear, after the certification process was halted when Donald Trump supporters stormed the building.

"We have decided we should proceed tonight at the Capitol once it is cleared for use," Pelosi said in a letter to colleagues, after reports that the building was secured by police and demonstrators were removed.

The senior lawmaker blasted the storming of the Capitol as a "shameful assault" on American democracy that was "anointed at the highest level of government, but said "it cannot, however, deter us from our responsibility to validate the election of Joe Biden."