Republican presidential candidate Donald Trump was forced to walk to his party's convention in California after protests erupted in San Francisco.

To avoid several hundred demonstrators the billionaire businessman was forced to halt his motorcade and, guided by secret service agents, cross a freeway and pass through a barrier in a fence to access the hotel where the convention was taking place.

Trump's rallies have been disrupted by protesters in many cities across America for months now but they have rarely escalated into mass street demonstrations.

The reality TV star campaigned to block illegal immigrants entering the US and he referenced them when he spoke to supporters at the rally.

“That was not the easiest entrance I've ever made. My wife called, she said ‘there was helicopters following you’, and then we went under a fence and through a fence.

“It felt like I was crossing the border actually. It's true, I was crossing the border, but I got here."

Local police said five people were arrested following the demonstrations.

Trump is moving closer to winning the Republican nomination after a string of victories this week however California is a key state where his rivals could disrupt his momentum.

He is the only candidate left on the Republican side who could possibly clinch the nomination through the regular voting process. Yet he could still fall short of the 1,237 delegates he needs to secure the nomination outright.

The other candidates, Ted Cruz and John Kasich, are desperately trying to keep Trump from that threshold in order to push the race to a contest at the Republican National Convention in July.

This week the Texas senator and Ohio governor even took the rare step of announcing plans to coordinate in upcoming contests to try to minimize Trump's delegate totals.