A witness said he spotted a man with a rifle on a rooftop shortly before shots were fired at Donald Trump during a rally in Pennsylvania.

Greg Smith told the BBC that the man had crawled on top of a building and that he reported it to the police.

“I’m thinking to myself ‘Why is Trump still speaking, why have they not pulled him off the stage’… the next thing you know, five shots ring out,” he said.

Smith said he saw the gunman around five minutes into Trump’s speech.

“We noticed the guy bear-crawling up the roof of the building beside us, 50ft away,” he said. “He had a rifle, we could clearly see a rifle.

“We’re pointing at him, the police are down there running around on the ground, we’re like ‘Hey man, there’s a guy on the roof with a rifle’… and the police did not know what was going on.”

He said he tried to alert the authorities for three to four minutes, but thought they probably couldn’t see the gunman because of the slope of the roof.

“Why is there not Secret Service on all of these roofs here?” he asked. “This is not a big place. “[It’s a] security failure, 100% security failure.”

Smith said his child was “crying and begging me to take him home” after the shooting.

“There were a lot of kids up there with us who were terrified, they’re still terrified,” he said.

The FBI is treating the shooting as an attempted assassination.

The suspected shooter, who has been named by the FBI as Thomas Matthew Crooks, was shot dead shortly afterwards. A crowd member was also killed and two others were critically injured.