A man who sparked a security scare at a Donald Trump rally in Nevada said he was tackled by the candidate's supporters when he held up a "Republicans against Trump" sign.

Mr Trump was addressing the crowd in Reno today when he was bundled off the stage by three Secret Service agents amid a commotion in the audience.

The protester, who identified himself as Austyn Crites, told NBC News he came armed "with just one sign that said 'Republicans against Trump.'"

He told The Guardian that he was knocked to the ground, punched, kicked and choked by Mr Trump's supporters when he attempted to silently hold up the sign.

"I'm actually a Republican ... but I just don't support Donald Trump," Mr Crites told reporters after he was released by police.

Mr Crites, 33, said that he agreed with Mr Trump on many issues, but added: "I believe that he's very dangerous for the country."

On social media, Trump supporters pilloried him as a Hillary Clinton mole, pointing to what they said was his deleted pro-Hillary Facebook page.

Mr Crites told The Guardian that he believes the Democratic candidate is the only person who can stop Mr Trump, and said that he briefly canvassed for her campaign.

Trump was whisked away by secret service after a security scare.

The Secret Service said its agents sprang into action after someone had shouted "gun".

"In front of the stage, an unidentified individual shouted 'gun,'" the service said in a statement.

"Secret Service agents and Reno Police Officers immediately apprehended the subject. Upon a thorough search of the subject and the surrounding area, no weapon was found.

"A thorough investigation is ongoing at this time by the US Secret Service and the Reno Police Department.”

Secret Service rushed in after they said a man shouted "gun".

Supporters could also be seen trying to flee the area as Mr Trump was whisked off stage, and a man in the crowd was arrested.

A short time later, Mr Trump returned to the stage and thanked the Secret Service for protecting him.

"Nobody said it would be easy for us," Mr Trump said.

"But we will never be stopped. Never. Ever.

"I want to thank the Secret Service. They don’t get enough credit. They are amazing people."

Just before the scare Mr Trump could be seen shielding his eyes from the lights in order to peer into the crowd.

There were signs of a struggle in the crowd as the agents led Mr Trump away, shielding his body.

Footage shows a large number of police and other security officials arresting one man.