The murder of the 67-year-old, who had been Japan's longest-serving leader, stunned the nation and prompted an international outpouring of grief and condemnation.

It was all the more shocking given Japan's strict gun laws and low rates of violent crime, with Prime Minister Fumio Kishida describing it as a "barbaric act" that was "absolutely unforgivable."

Abe was shot shortly before noon while campaigning in the western region of Nara ahead of weekend upper house elections.

He was flown by helicopter to the Nara Medical University hospital where he was pronounced dead several hours later.

"Shinzo Abe was transported to (the hospital) at 12:20 pm. He was in a state of cardiac arrest upon arrival," said Hidetada Fukushima, professor of emergency medicine at the hospital.

"Resuscitation was administered. However, unfortunately he died at 5:03 pm."

Fukushima said Abe had suffered two gunshot wounds to the neck and died of massive blood loss, despite being administered enormous transfusions.

A visibly emotional Kishida told reporters  after Abe's death was confirmed that he was "lost for words".

He earlier abandoned the campaign trail and flew to Tokyo by helicopter where in a quivering voice he condemned "a barbaric act during election campaigning, which is the foundation of democracy."

"It is absolutely unforgivable. I condemn this act in the strongest terms."

The attack occurred as Abe delivered a stump speech with security present, but spectators able to approach him easily.

Footage broadcast by NHK showed him standing on a stage when a man dressed in a grey shirt and brown trousers approached from behind, before drawing a weapon from a bag and firing.

At least two shots appear to be fired, each producing a cloud of smoke.

As spectators and reporters ducked, a man was shown being tackled to the ground by security and he was arrested.

Local media identified the man as 41-year-old Tetsuya Yamagami, citing police sources, with several media outlets describing him as a former member of the Maritime Self-Defense Force, the country's navy.

He was wielding a weapon described by local media as a "handmade gun", and NHK said he told police after his arrest that he "targeted Abe with the intention of killing him".

Witnesses at the scene described shock as the political event turned into chaos.

"The first shot sounded like a toy bazooka," a woman told NHK.

"He didn't fall and there was a large bang. The second shot was more visible, you could see the spark and smoke."

Officials from the local chapter of Abe's Liberal Democratic Party said there had been no threats before the incident and that his speech had been announced publicly.

Several parties announced their senior members would halt campaigning in the wake of the attack, but the LDP and coalition partner Komeito later announcing that canvassing would resume on Saturday.

The attack prompted international shock, with European Commission chief Ursula von der Leyen tweeting that the "brutal and cowardly murder" had shocked the world.

"The deadly attack on Shinzo Abe has left me aghast and deeply sad," German Chancellor Olaf Scholz said.

South Korean President Yoon Suk-yeol described the killing as an "unacceptable act of crime".

Abe held office in 2006 for one year and again from 2012 to 2020, when he was forced to step down due to the debilitating bowel condition ulcerative colitis.

He was a hawkish conservative who pushed for the revision of Japan's pacifist constitution to recognise the country's military and has stayed a prominent political figure even after his resignation.

Japan has some of the world's toughest gun-control laws, and annual deaths from firearms in the country of 125 million people are regularly in single figures.

Getting a gun licence is a long and complicated process for Japanese citizens, who must first get a recommendation from a shooting association and then undergo strict police checks.

Corey Wallace, an assistant professor at Kanagawa University who focuses on Japanese politics, said the incident recalled the 1960 assassination of Inejiro Asanuma, the leader of the Japan Socialist Party, who was stabbed by a right-wing youth.

He noted that Japanese politicians and voters were used to a personal and close-up style of campaigning.

"This could really change," he said.