US Vice-President Kamala Harris has passed the threshold to clinch the Democratic presidential nomination in a vote of party delegates.

Speaking by telephone, Ms Harris said she was "honoured to be the presumptive nominee" as the virtual roll call continues ahead of the Democratic National Convention (DNC) in Chicago later this month.

Ms Harris is the first black woman and first South Asian woman to become the White House standard-bearer for a major US political party.

She is expected to name her running mate by Monday.