A man found illegally in possession of a shotgun and a loaded handgun was arrested by sheriff's deputies assigned to protect a Donald Trump rally in Coachella, California, the Riverside County sheriff's office announced on Sunday.

It said the deputies, manning a checkpoint near the rally, arrested 49-year-old Vem Miller of Las Vegas as he drove up in a black SUV.

They later booked him at a local detention centre on charges of possessing a loaded firearm and a high-capacity magazine.

"This incident did not impact the safety of former President Trump or attendees of the event," the statement said.

The sheriff's office offered no immediate information on Miller's intentions.

He was released on bail and faces a court hearing on January 2.

But coming on the heels of two assassination attempts -- one in Pennsylvania in which a bullet grazed Trump's ear, and a second, aborted attempt at his Florida golf course -- the arrest raised concerns.

There was no immediate comment from either the Trump campaign or the US Secret Service, which is charged with protecting top officials and candidates. (AFP)