"He loved this country and always looked one step ahead of the times," Mr. Kishida said. "He was a great politician who left many achievements in terms of developing the future of the country in various fields. To lose him in such a way is a great sadness."
The premier said the vote July 10 would go ahead as planned and his government would do its utmost to ensure security, adding elections are the foundation of democracy. The LDP's ruling bloc had been expected to keep its majority in the upper house even before the shock.
Leaders from across the world paid tribute to Mr. Abe, who was a defining and sometimes divisive figure for Japan as the country navigated economic stagnation and China's rise next door. He was a security hawk, a fiscal dove, a defender of Japan's alliance with the U.S. and an advocate for maintaining the postwar global order.
Indian Prime Minister Narendra Modi praised Mr. Abe as "a towering global statesman, an outstanding leader and a remarkable administrator." U.S. Secretary of State Antony J. Blinken called Mr. Abe an "extraordinary partner" whose death was "profoundly disturbing in and of itself, it's also such a strong personal loss for so many people."
Former U.S. President Donald Trump, whose favor Mr. Abe sought to gain early on, called the fallen premier a "true friend of mine and, much more importantly, America." While some nationalists in China cheered Mr. Abe's death, the Chinese government expressed "shock" and offered its condolences for a leader whom it said had made contributions to improving ties between the two rivals.
The initial market reaction to the news that Mr. Abe had been shot was a rush to haven assets. The yen climbed alongside U.S. Treasuries, with the currency rising as much as 0.5% against the dollar.
The person suspected of shooting Mr. Abe was identified by local media as Tetsuya Yamagami, a local 41-year-old veteran of the Japan Maritime Self-Defense Force. He told police he intended to kill Mr. Abe because of frustration with the former premier, national public broadcaster NHK said, adding that investigators removed explosives from his home after a search.
The incident was one of Japan's highest profile acts of political violence since World War II. World leaders extended condolences for Mr. Abe, who spent more time as premier than anyone since Japan established the office in the 1880s.
"He was the single most powerful politician in Japan. He clearly had the ability to set the political agenda in ways that others — including Kishida — do not," said Tobias Harris, a senior fellow for Asia at the American Progress think tank who has written a biography of Mr. Abe.
Japan is a country with some of the strictest gun laws among leading economies and shootings are rare. But political violence still occurs from time to time: In 2007, Iccho Ito, the mayor of Nagasaki, died after being shot twice by a member of an organized crime gang. The last time a current or former Japanese prime minister was shot was 90 years ago.
There were few details about the weapon used in the attack on Mr. Abe. Video from the scene showed what appeared to be two long tubes wrapped together with black tape on the ground at the scene.
Mr. Abe's record-setting run brought stability to Japan after a revolving door of six administrations, including a previous stint where he served as leader. Mr. Abe helped Japan escape from a cycle of deflation, endured a Trump administration that questioned the nation's only military alliance, and worked to improve ties with its biggest trading partner China, which were at their most hostile in decades when he took office.
The first Japanese premier born after the country's defeat in World War II — and a vocal defender of its postwar record — Mr. Abe sought to end apologies for past imperialism and reinterpreted the country's pacifist constitution to loosen restrictions on the military. He nonetheless managed to stabilize relations with China, where a wave of anti-Japanese protests had raged in the weeks before his second election as leader.
Mr. Abe also devoted energy to trying to resolve a World War II territorial dispute with Russia, which has simmered for seven decades, lavishing hospitality on Vladimir Putin, in a policy that was reversed following the Russian invasion of Ukraine.
Mr. Abe is perhaps best known for his plans to revive Japan's flagging economy through unprecedented monetary easing and regulatory reform that was eventually labeled "Abenomics." He has been seen as a steady hand who consolidated power during his record run and was able to overcome scandals, including one that came to light in 2017 over questionable government land allocations for schools provided to associates of Mr. Abe and his wife, Akie.
Longtime Bank of Japan Governor Haruhiko Kuroda, a key partner in implementing Mr. Abe's economic vision, said he felt "very sorry" for his former colleague's passing.
"Former Prime Minister Abe has achieved many results toward the end of prolonged deflation and sustainable economic growth," Mr. Kuroda said. "I pay sincere tribute to his strong leadership and dedication to our economy."