Japan's former prime minister Shinzo Abe has been shot while campaigning in the city of Nara, a government spokesman says, with public broadcaster NHK reporting he appeared to have been fired at from behind by a man with a shotgun.
Chief Cabinet Secretary Hirokazu Matsuno said he did not know Abe's condition.
Kyodo news agency and NHK said Abe, 67, appeared to be in a state of cardiac arrest when taken to hospital.
Shots were heard and a white puff of smoke was seen as Abe made a stump speech for a Sunday upper house election outside a train station in the western city, some 480km from the capital Tokyo, NHK said.
An NHK reporter on the scene said they heard two consecutive bangs during Abe's speech.
Police arrested a male suspect at the scene, NHK said.
Matsuno, told a briefing Abe had been shot at about 11.30am (12.30pm AEST), adding, "Such an act of barbarity cannot be tolerated".
TBS Television reported Abe had been shot on the left side of his chest and apparently also in the neck.
Abe served two terms as prime minister to become Japan's longest-serving premier before stepping down in 2020 citing ill health.
He has remained a dominant presence over the ruling Liberal Democratic party party, controlling one of its major factions.
His protege, Prime Minister Fumio Kishida, goes into an upper house election on Sunday hoping, analysts say, to emerge from Abe's shadow and define his premiership.
Kishida suspended his election campaign after Abe's shooting and was returning to Tokyo, media reported.
The United States ambassador, Rahm Emanuel, said he was saddened and shocked by the shooting of an outstanding leader and unwavering ally.
Abe is best known for his signature Abenomics policy, which featured bold monetary easing and fiscal spending.
He also bolstered defence spending after years of decline and expanded the military's ability to project power abroad.
In a historic shift in 2014, his government reinterpreted the post-war, pacifist constitution to allow troops to fight overseas for the first time since World War II.
The following year, legislation ended a ban on exercising the right of collective self-defence, or defending a friendly country under attack.
Abe, however, did not achieve his long-held goal of revising the US-drafted constitution by writing the Self-Defence Forces, as Japan's military is known, into the pacifist Article 9.
He was instrumental in winning the 2020 Olympic Games for Tokyo, cherishing a wish to preside over the global event, which were postponed by a year to 2021 because of the COVID-19 pandemic.
Abe first took office in 2006 as Japan's youngest prime minister since World War II.
After a year plagued by political scandals, voter outrage at lost pension records, and an election drubbing for his ruling party, Abe quit citing ill health.
He became prime minister again in 2012.
Abe hails from a wealthy political family that included a foreign minister father and a great-uncle who served as premier.
The details of this report are developing. It will be updated.
