US Republican presidential candidate Donald Trump was rushed off the stage by Secret Service agents on Saturday (local time) during a rally in Reno, Nevada following a commotion in the crowd.
Before the incident, Mr Trump had been talking to a protester in the crowd.
"We have one of those guys from the Hillary Clinton campaign here. How much are you being paid? $1500? Alright. Take him out."
About 15 seconds later, Mr Trump was whisked offstage. He re-emerged several minutes later to cheers from the crowd.
"Nobody said it was going to be easy for us, but we will never be stopped," he said. "We will never be stopped. I want to thank the Secret Service. These guys are fantastic."
The commotion began when someone yelled "gun!" after someone held up a sign in the crowd, Trump campaign representatives told ABC News.
No weapon was discovered, law enforcement officials told CNN.
A team of SWAT unit police was seen at the front of the crowd moments after Mr Trump was taken offstage.
At least one man was taken away by police and Secret Service members.
Mr Trump later issued a statement.
"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!"