Washington: US Senator Bernie Sanders won the Democratic presidential primary in New Hampshire, giving a big boost to his campaign for the 2020 White House bid as the race to his party's nomination gathers momentum over the next few months.

Sanders, 78, who lost to former secretary of state Hillary Clinton in the 2016 presidential primaries in New Hampshire was ahead of his closest rival Pete Buttigieg. With more than 85 per cent of the votes counted, the Senator from Vermont took 26 per cent support, followed by Buttigieg closely with 24.4 per cent and Amy Klobuchar coming third with 19.8 per cent of the votes.