Two people, including the gunman, are reportedly dead, and two others are critically injured, in a shooting at a Trump rally in Pennsylvania.

The former president was at his last rally before the Republican National Convention opens Monday when apparent gunshots were heard, before the presumptive Republican nominee reached for his right ear and ducked for cover behind the stand.

He was seen being escorted to a car by security personnel with what appeared to be blood on his face.

Know the news with the 7NEWS app: Download today

Reuters reported that one person is believed to be dead, according to Pittsburgh ABC affiliate WTAE, who cited Butler County District Attorney Richard Goldfinger. CNN reports the gunman was “neutralised”.

The Washington Post, citing sources, reports an audience member was also killed.

Two other audience members are believed to have been critically injured, CNN reports.

Australian Prime Minister Anthony Albanese said security agencies will be examining the event.

“There is a great deal of cooperation... between Australia and the United States, and I am sure there will be lessons to be learned,” he told reporters on Sunday.

“I say again, though, we must lower the temperature of the debate... there is nothing to be served by some of the escalation of rhetoric that we see in some of our political debate.”

Albanese added, we should “be able to have political discussion and do it respectfully”.

“This is a time for unity...it’s a time for calm, it’s a time for allowing the authorities in the United States to do their jobs,” he said.

Meanwhile, US president Joe Biden said he had been “briefed on the shooting”, and that he was “grateful” to hear that Trump was “doing well”.

“I’m praying for him and his family and for all those who were at the rally, as we await further information.

“Jill and I are grateful to the Secret Service for getting him to safety. There’s no place for this kind of violence in America. We must unite as one nation to condemn it.”

At a brief press conference, he said he had “opinions” on whether the shooting was an assassination attempt but would wait for official word.

“I have an opinion but I don’t have any facts. I want to make sure we have all the facts before I make any more comments.”

World leaders have condemned the attack.

British Prime Minister Keir Starmer said he was “appalled”.

“We send him and his family our best wishes.

“Political violence in any form has no place in our societies and my thoughts are with all the victims of this attack.”

Pennsylvania Senator, Bob Casey, offered the support of the state police in response to the incident.

“I am monitoring the situation at President Trump’s rally in Butler, and I’ve reached out to the State Police to offer support,” he said.

“Political violence is never acceptable, and I am hoping former president Trump and all attendees are safe. Everyone in Butler should listen to law enforcement.”

Israeli Prime Minister Benjamin Netanyahu said he had been “shocked” by the news.

“Sara and I were shocked by the apparent attack on President Trump. We pray for his safety and speedy.”

Prime Minister Anthony Albanese has commented that the events were “concerning”.

“The incident at former President Trump’s campaign event in Pennsylvania today is concerning and confronting,” he said.

“There is no place for violence in the democratic process.

“I am relieved to hear reports that former President Trump is now safe.”