WASHINGTON (AFP) - Anti-Donald Trump protesters blocked a major thoroughfare Saturday in Arizona in an attempt to prevent supporters of the Republican presidential frontrunner reaching a rally he was due to hold.

It was just the latest attempt by opponents of the bombastic billionaire to disrupt his campaign for the White House, with demonstrations and violence breaking out at several Trump events in the past week.

Police were threatening to make arrests to break up the estimated 50 protesters - who held a banner across the width of Shea Boulevard with the words "Dump Trump" - as long lines of traffic backed up in Fountain Hills, on the outskirts of Phoenix.

Controversial Maricopa County Sheriff Joe Arpaio, who openly endorsed and supports Trump, said he would do everything possible to ensure the rally would go ahead.

Deputy Joaquin Enriquez told CNN: "We have a group of anti-Trump protesters who have used their vehicles to block Shea Boulevard, which is a major artery into the town."

"Obviously the sheriff's office is going to treat and wants this to be a peaceful protest," he added.

"However, when they block a major artery, they're causing safety hazards, emergency vehicles need to enter and exit this way, so this is causing a huge issue for us considering there's backing up."