US President Donald Trump has ordered an FBI investigation into sexual misconduct allegations against his US Supreme Court nominee Brett Kavanaugh, throwing his confirmation into doubt.

A Senate committee voted on Friday to approve Kavanaugh's nomination to the top US court. But a Republican member only backed the move on the understanding that such an inquiry would occur, the US media reported. As a result, a full Senate vote on Kavanaugh's confirmation has been delayed for up to a week. He has been accused of sexually assaulting Christine Blasey Ford, a professor of psychology in California, in the 1980s.