Hillary Clinton has opened up a popular vote lead of almost 400,000, as president-elect Trump continues to transition to his first term in the Oval Office.

Trump seized a shock victory on Tuesday, 8 November, winning swing states including Ohio and Florida as well as traditionally Democrat states such as Pennsylvania and Wisconsin, in a 290-232 electoral college victory.

However Democrat Hillary Clinton has opened up a commanding lead in the popular vote, with 60,467,245 to Trump's 60,071,650, or 47.7 per cent to 47.4 per cent of the vote respectively.

Her lead in the popular vote has increased from the 233,000 lead she had on Thursday, according to data from CNN and NBC.

Though a commanding lead, it is less than the record 547,398 popular vote victory of losing presidential candidate Al Gore in the 2000 election.

The results in Michigan and New Hampshire have yet to be called.

Retiring Senate Minority leader Harry Reid took aim at Trump on Friday, branding the president-elect a "a sexual predator who lost the popular vote".

"The election of Donald Trump has emboldened the forces of hate and bigotry in America," Reid said in a statement Friday. "White nationalists, Vladimir Putin and ISIS are celebrating Donald Trump's victory, while innocent, law-abiding Americans are wracked with fear."

The statements contrasts with that of other leading Democrats, who have stressed the need for national unity in the wake of Trump's win.

President Barack Obama said he was "encouraged" after discussions on the transition of power with Trump at the White House on Thursday.

Under the US electoral system, voters choose representatives in the electoral college who in turn vote for the president. The number of electors in a region is determined by its population.

Critics have called for the system to be reformed, arguing it is undemocratic.