Donald Trump rushed off stage by Secret Service at Nevada rally.

US Republican presidential candidate Donald Trump has been hustled off stage by security agents at a rally in Reno, Nevada, after a perceived threat in the crowd.

The incident began when Mr Trump noticed what he considered a heckler, saying it was someone “from the Hillary Clinton campaign”.

A few seconds later people near the stage began pointing at someone in the crowd near the front.

Two security agents grabbed Mr Trump by the shoulders and rushed him backstage.

The threat was unclear, but police officers swarmed over a white male in the front of the crowd and held him face down on the ground while they searched him.

Moments later, the man was escorted away by police with his hands behind his back.

A CNN reporter at the event who spoke to witnesses to the incident said no one saw a weapon.

Mr Trump released a statement thanking the Secret Service for their assistance.

“I would like to thank the United States Secret Service and the law enforcement resources in Reno and the state of Nevada for their fast and professional response,” he said.

“I also want to thank the many thousands of people present for their unwavering and unbelievable support.

“Nothing will stop us —we will make America great again!”

Mr Trump returned to the stage a short while later to continue his rally speech at the Reno convention centre, which drew thousands of supporters.

“Nobody said it was going to be easy for us. But we will never be stopped. Never ever be stopped,” Mr Trump said.

Trump accuses officials of keeping poll sites open late in Nevada

The incident occurred as both candidates are making their closing arguments to American voters, crisscrossing the US in hopes of convincing last-minute undecided voters.

He is accusing officials of wrongly keeping polling sites open late in Nevada’s Clark Country in order to boost Democratic early-voting turnout.

There appears to be no evidence that is the case.

He also continued to mock his rival Hillary Clinton’s star-studded get-out-the-vote events, saying that she needs to appear alongside celebrities or else nobody will attend her events.

Mrs Clinton has leaned on her celebrity supporters to draw large crowds in the final days of the campaign.

She faced dark skies in Florida, fighting intense rain and wind in a key battleground state before a Pennsylvania appearance with pop singer Katy Perry.

She was also preparing to campaign Sunday (local time) with basketball superstar LeBron James, having shared the stage the night before with singer Beyonce and rapper Jay Z.

Opinion polls show Mrs Clinton still holds advantages in states that could be critical in deciding the election.

But her lead has narrowed after a revelation a week ago that the Federal Bureau of Investigation was looking into a new trove of emails as part of its probe into her handling of classified information while she was secretary of state.

Reuters/AP

This post originally appeared on ABC News.