Bernie Sanders has easily won Democratic nominating contests in Alaska, Washington and Hawaii, chipping away at Hillary Clinton's commanding lead in the race to pick the party's candidate for the White House.

Mr Sanders still faces a steep climb to overtake Mrs Clinton, but the big victories in Saturday's caucuses generated more momentum for his campaign and could stave off calls from Democratic leaders that he should wrap up his bid in the name of party unity.

US news networks showed Sanders winning by wide margins in Saturday's caucus votes in all three western states.

In Washington — the biggest prize with 101 delegates up for grabs — Mr Sanders won with an estimated 72.1 per cent, against 27.7 for Mrs Clinton.

In Hawaii, 71 per cent of Democratic caucus-goers supported Mr Sanders, against 29 per cent for Mrs Clinton.

In Alaska, Mr Sanders' margin of victory was 79.2 percent, against 20.8 percent for Mrs Clinton.

The 74-year-old Vermont senator celebrated his victories via Twitter late Saturday.

"Thank you, Alaska! Together we are sending a message that this government belongs to all of us," he wrote.

Appearing at a campaign rally in Wisconsin, Mr Sanders said his wins were proof that the tide was turning in his favour as the campaign moves west.

"It is hard for anybody to deny that our campaign has the momentum," Mr Sanders told cheering supporters.

Clinton leads race by 300 delegates

Mrs Clinton, the former secretary of state, has increasingly turned her attention toward a potential November 8 general election showdown against Republican frontrunner Donald Trump, claiming she is on the path to wrapping up the nomination.

Heading into voting on Saturday (local time), she led Mr Sanders by about 300 pledged delegates in the race for the 2,382 delegates needed to win the nomination at July's convention.

Adding in the support of superdelegates — party leaders who are free to back any candidate — she has 1,690 delegates to Mr Sanders' 946.

Mr Sanders needs to win up to two-thirds of the remaining delegates to catch Mrs Clinton, who will keep piling up delegates even when she loses under a Democratic Party system that awards delegates proportionally in all states.

The presidential hopeful has repeatedly said he is staying in the race until the convention, pointing to big crowds at his rallies and high voter turnout among young and first-time voters as proof of his viability.

After raising $US140 million, he has the money to fight on as long as he wants.

Mr Sanders has energised the party's liberal base and young voters with his calls to rein in Wall Street and fight income inequality, a message that played well in liberal Washington and the other Western states. Mr Sanders won in Utah and Idaho earlier this week.

All three contests on Saturday were caucuses, a format that has favoured Mr Sanders because it requires more commitment from voters, and were in states with fewer of the black and Hispanic voters who have helped fuel Mrs Clinton's lead.

The Democratic race now moves to contests in Wisconsin on April 5 and in New York on April 19. There were no contests on Saturday in the Republican race featuring Mr Trump and rivals Ted Cruz and John Kasich.



Reuters/AFP