Former Japanese Prime Minister Shinzo Abe has died, according to Japan's national broadcaster.

Abe died in the hospital where he was receiving medical treatment, near to the attack in Nara, a senior Liberal Democratic Party official said, public broadcaster NHK reports.

Abe was in heart failure after being shot during a campaign speech on Friday in western Japan, NHK public television said.

Abe sustained wounds on the right side of his neck and left clavicle after being shot, Nara city Fire Department confirmed.

A man, centre, is detained near the site of gunshots in Nara, western Japan. Photo / AP

Earlier reports said Abe is showing no vital signs and "appears to be in a state of cardio-respiratory arrest". The news agency states the term is "used in Japan before a feared death can be confirmed by a doctor".

The broadcaster aired footage showing Abe collapsed on the street, with several security guards running toward him. Abe was holding his chest when he collapsed, with his shirt smeared with blood. NHK says Abe was rushed to a hospital.

Police arrested 41-year-old Yamagami Tetsuya in Nara City for allegedly attempting murder and say a gun was seized at the site, NHK reported.

Abe was in Nara, 480km west of Tokyo, campaigning ahead of Sunday's election for the parliament's upper house and was giving a speech when people heard a gunshot.

The attack was a shock in a country that's one of the world's safest and with some of the strictest gun control laws anywhere.

The term heart failure means the heart cannot sufficiently pump blood and supply necessary oxygen to the rest of the body. In Japan, officials sometimes use the term to describe situations where victims are no longer alive but before a formal declaration of death has been made.

It was not immediately clear how serious Abe's injuries were or if he was still displaying vital signs.

"Former prime minister Abe was shot at around 11.30am," in the country's western region of Nara, chief cabinet secretary Hirokazu Matsuno told reporters.

"One man, believed to be the shooter, has been taken into custody. The condition of former prime minister Abe is currently unknown."

"Whatever the reason, such a barbaric act can never be tolerated, and we strongly condemn it," Matsuno added.

Prime Minister Jacinda Ardern put out a statement saying she was "deeply shocked" to hear about Abe.

"Shinzo Abe was one of the first world leaders I met when I became Prime Minister. He was always focused and thoughtful, but also generous. I remember after our first bilateral meeting as we were waiting for an official photo he leaned over to tell me he was sorry that my cat had passed away.

"In the meetings we had over the years, I saw a statesman, someone who helped usher through complex negotiations like the CPTPP, but also someone who was thoughtful and kind. The longest serving Prime Minister of Japan, whose loss will be deeply felt by so many- our thoughts and aroha are with you all."

Former PM John Key said: "It is with great sadness that I learned of Former PM Abe's death. Over his time as PM I worked closely with PM Abe on a variety of issues including TPP. I always found him to be engaging thoughtful and a good friend of NZ."

Key was PM when Abe became PM of Japan in 2012.

Former PM Helen Clark said Abe was a "towering figure" in Japanese politics.

New Zealand First leader Winston Peters said in a statement:" It is with great sorrow that we have learnt of the passing of the former Prime Minister of Japan Shinzo Abe.

"Shinzo Abe was Japan's longest serving Prime Minister and his presence and influence was critically important to Japan's leadership on the international stage, particularly on issues such as the CPTPPA and the indo-pacific concept. He established very meaningful and warm relationships with many nations and in doing so gave Japan a heightened presence and importance.

"Our sincere condolences go to his wife Akie, his family, and indeed the entire Japanese nation."

Australia's new prime minister Anthony Albanese also offered his thoughts to Abe's family and the people of Japan. "Shocking news from Japan that former PM Shinzo Abe has been shot - our thoughts are with his family and the people of Japan at this time," he tweeted.

This aerial photo shows the scene of gunshots in Nara, western Japan. Photo / AP

Abe, 67, stepped down as prime minister in 2020 because he said a chronic health problem has resurfaced. Abe has had ulcerative colitis since he was a teenager and has said the condition was controlled with treatment.

He told reporters at the time that it was "gut wrenching" to leave many of his goals unfinished. He spoke of his failure to resolve the issue of Japanese abducted years ago by North Korea, a territorial dispute with Russia and a revision of Japan's war-renouncing constitution.

That last goal was a big reason he was such a divisive figure.

His ultra-nationalism riled the Koreas and China, and his push to normalise Japan's defence posture angered many Japanese. Abe failed to achieve his cherished goal of formally rewriting the US-drafted pacifist constitution because of poor public support.

Supporters of Abe said that his legacy was a stronger US-Japan relationship that was meant to bolster Japan's defence capability. But Abe made enemies too by forcing his defense goals and other contentious issues through parliament, despite strong public opposition.

Abe is a political blue blood who was groomed to follow in the footsteps of his grandfather, former Prime Minister Nobusuke Kishi. His political rhetoric often focused on making Japan a "normal" and "beautiful" nation with a stronger military and bigger role in international affairs.

US Ambassador to Japan Rahm Emanuel expressed sadness and shock at the shooting. "Abe-san has been an outstanding leader of Japan and unwavering ally of the US. The US Government and American people are praying for the well-being of Abe-san, his family, & people of Japan," he said on Twitter.