During a campaign rally in the city of Butler in the state of Pennsylvania, shot at the former US president and presidential candidate from the Republican Party, Donald Trump, US media reported.

According to Reuters, Trump was shot in the ear.

His face was drenched in blood. His security agents surrounded him once Trump stepped to the platform and shouted, "Fight back!" three times.

The shooter is dead, one rally attendee was killed and two other attendees were injured, the Secret Service said in a statement. The incident is being investigated as attempted murder.

Law enforcement officials told reporters they have tentatively identified the alleged shooter but are not ready to make that public. They also said they have not yet established a motive. The 78-year-old Trump had just started his speech when the shots rang out.