It wasn't much of a contest, but presumptive GOP presidential candidate Donald Trump chalked up an easy win in the Republican primary in Washington state, where his rivals had already dropped out.

However, the primary was overshadowed by hard clashes between hundreds of anti-Trump protesters and police outside the candidate's rally at the convention centre in Albuquerque, New Mexico.

Protesters, many of whom were waving Mexican flags, busted through police barricades, lit fires and hurled rocks at the city's convention centre, even smashing one of the building's doors. Proetesters reportedly taunted police and jumped on to police vehicles, while drivers of cars and trucks were 'wheel-spinning' their car tyres on the street to create more noise and smoke.

"We need to make sure that he knows that we do not accept the message that he's bringing and the hatred," Juan Sanchez, of the Democratic Party of New Mexico, told KRQE-TV.

Officers in riot gear and mounted on police horses forced the protesters away from the convention centre as anti-Trump chants filled nearby streets.

Inside the convention center, Trump was interrupted several times by protesters, many of whom were arrested.

"We're going to build a wall" between the US and Mexico, declared Trump again to thousands cheering inside the convention centre. "It's going to be a real wall. It's going to be a wall that's going to make ceiling look low and that ceiling's quite high."

However, one place definitely not giving Trump any trouble was Washington state.

With nearly 70% of the vote counted in Washington, Trump had 76.2% support. Senator Ted Cruz grabbed 10.1% and Ohio Governor John Kasich nabbed 9.9%.

The 44 delegates at stake in Washington will be a few shy of the 1,237 Trump needs to clinch the GOP nomination. But he is bound to clean up in upcoming contests on 7 June in California, New Jersey, New Mexico, Montana and South Dakota.

Trump made a brief phone call to a group of cheering supporters in Lynnwood, Washington, before the vote count, and he vowed to win the state in the general election, the Seattle Times reported.

"I'm going to be there a lot. We're going to campaign hard to win," Trump said. And while Washington has traditionally been known as a Democratic state, Trump vowed: "Not with us; it's going to be Republican."

On the Democratic side of the ledger, Hillary Clinton beat Bernie Sanders with nearly 54% of the vote. Democrats are ignoring the result, though, as the party had already allocated presidential delegates based on March caucuses.