Chao, the wife of Senate Republican Leader Mitch McConnell, said in an email to staff on Thursday that the mob attack "has deeply troubled me in a way that I simply cannot set aside". She said her resignation will take effect on Monday.

In a letter to Trump, DeVos said the attack on the Capitol was unconscionable. "There is no mistaking the impact your rhetoric had on the situation, and it is the inflection point for me," she wrote, adding her resignation would be effective Friday.

The White House did not immediately respond to a request for comment on DeVos's resignation.

With less than two weeks left of Trump's presidency, many aides were already heading for the door, but the sudden exodus suggested revulsion among some over his encouragement of supporters who brought chaos to the Capitol on Wednesday in an ultimately futile bid to prevent formal certification of Democrat Joe Biden's election victory.

Deputy national security adviser Matt Pottinger, a leading aide on Trump's China policy, quit abruptly on Wednesday, said a senior administration official.

He was followed by Ryan Tully, senior director for European and Russian affairs at the National Security Council, said a second senior official.

The Republican Trump's pledge on Thursday of an "orderly transition" on Jan. 20 was partly intended to head off further resignations, but the second official told Reuters: "It's not going to stop it."

The images at the Capitol filled television screens worldwide, forever marking Trump's presidency.

Chao, a labour secretary and deputy transportation secretary under previous Republican presidents, has led the department for four years. In an interview with Reuters on December 31, Chao said she planned to remain through January 20.

On Thursday, she said "we will help my announced successor, Mayor Pete Buttigieg, with taking on the responsibility of running this wonderful department".

Chao made the announcement a day after McConnell condemned the violence and the effort by some Republican lawmakers to block certification of Biden's victory. Trump has sought unsuccessfully to overturn the results with unfounded claims of widespread voter fraud.

Mick Mulvaney, a former White House chief of staff, resigned as special envoy to Northern Ireland, telling CNBC: "I wouldn't be surprised to see more of my friends resign over the course of the next 24 to 48 hours."

John Costello, deputy assistant secretary at the Commerce Department, announced his departure in a blistering tweet, writing, "yesterday's events were an unprecedented attack on the very core of our democracy - incited by a sitting president".

First lady Melania Trump's chief of staff, Stephanie Grisham, also resigned on Wednesday. Two sources told Reuters that White House social secretary Rickie Niceta also quit, as did Sarah Matthews, a deputy White House press secretary.

Australian Associated Press