Hillary Clinton, Democratic candidate for US president, has publicly acknowledged her defeat to Republican rival Donald Trump in a concession speech.

"Last night I congratulated Donald Trump and offered to work with him on behalf of our country," she said. "I hope he will be a successful president for all Americans."

Clinton said the United States was "more deeply divided than we thought," telling her supporters they must accept the outcome of the election.

"We owe him an open mind a chance to lead," she said of Trump.

Clinton had a slim lead in the polls ahead of the vote. A polling average by tracker site RealClearPolitics gave her a 3.3-percentage point national lead.