Mourners lined the streets of central Tokyo on Tuesday to bid farewell to assassinated former Japanese prime minister Shinzo Abe, as his hearse was driven past political landmarks after a private funeral.

The country's longest-serving prime minister was gunned down on Friday while campaigning, in a crime that rattled Japan and prompted an outpouring of international condemnation and grief.

A private funeral is being held for Abe in Tokyo
A private funeral is being held for Abe in Tokyo AFP / Philip FONG

His funeral was held at Tokyo's Zojoji temple on Tuesday, with relatives and close acquaintances in attendance.

But elsewhere in the temple compound, thousands of well-wishers lined up in the humid heat to pay their respects before a photo of the late leader, who held office until 2020.

Abe was Japan's longest serving prime minister
Abe was Japan's longest serving prime minister AFP / Philip FONG

"I can't get over my sadness, so I came here to lay flowers," consultant Tsukasa Yokawa, 41, told AFP, describing Abe as "a great prime minister who did a lot to elevate Japan's presence" globally.

After the service, a hearse carrying Abe's body departed for a final tour of some of the political landmarks he served in: the parliament, the prime minister's office and the headquarters of his ruling Liberal Democratic Party.

Abe was gunned down on the campaign trail
Abe was gunned down on the campaign trail AFP / Charly TRIBALLEAU

Residents gathered along the route, while staff and officials, including ministers and senior LDP figures, stood sombrely outside each venue. They pressed their hands together and bowed their heads in respect as the car arrived.

Abe's widow Akie sat in the front of the hearse -- carrying her husband's mortuary tablet inscribed with his posthumous Buddhist name -- and bowed back.

Defence Minister Nobuo Kishi, Abe's brother, called the murder "an act of terrorism" on Tuesday.

Profile of Japan's former Prime Minister Shinzo Abe
Profile of Japan's former Prime Minister Shinzo Abe AFP / Janis LATVELS

"I've lost my brother. At the same time, Japan has lost an irreplaceable leader," he tweeted. "My brother loved Japan and risked his life to be a politician and protect this nation."

In a speech at the funeral, 81-year-old Deputy Prime Minister Taro Aso recalled drinking and playing golf with his close ally.

Abe's funeral was held at Zojoji temple in Tokyo where crowds gathered to see the hearse leave
Abe's funeral was held at Zojoji temple in Tokyo where crowds gathered to see the hearse leave AFP / Philip FONG

"You were supposed to read an eulogy for me. This is very painful," he said, according to Japanese media.

The hearse transporting Abe's body stopped briefly at the prime minister's office on a final tour of some of the political landmarks he served in during his career
The hearse transporting Abe's body stopped briefly at the prime minister's office on a final tour of some of the political landmarks he served in during his career POOL via AFP / Eugene Hoshiko

Abe was campaigning in the western city of Nara when he was shot.

The murder suspect, 41-year-old Tetsuya Yamagami, is in custody and has told police he targeted Abe because he believed the politician was linked to an organisation he resented.

Taiwanese vice president William Lai Ching-te (C) greets officials
Taiwanese vice president William Lai Ching-te (C) greets officials AFP / Philip FONG

Yamagami approached him from behind in broad daylight, in circumstances that have raised questions about security.

Satoshi Ninoyu, the chairman of the National Public Safety Commission, a cabinet position overseeing national police, pledged Tuesday to hold a full review of any security failings.

Local police have already admitted flaws in their guarding programme for the high-profile politician.

Police searches of the suspect's home have found pellets and other possible components for building a gun like the crude weapon used in the attack, Japanese media reported Tuesday, citing unnamed investigative sources.

Yamagami spent three years in Japan's navy and reportedly told investigators that his mother's large donations to a religious organisation had caused the family financial troubles.

The Unification Church, a global religious movement founded in Korea in the 1950s, said on Monday that Yamagami's mother was a member, but did not comment on any donations she may have made.

Foreign Minister Yoshimasa Hayashi said Tuesday that more than 1,700 condolence messages had been received from 259 countries, territories and international bodies.

On Monday, US Secretary of State Antony Blinken made a previously unscheduled stop in Tokyo to pay tribute to Abe, describing him as a "man of vision".

And Taiwanese Vice President William Lai was also in Tokyo for a surprise trip, Taiwanese media said.

China's foreign ministry hit out at the visit, accusing Taiwan authorities of using Abe's death as "an opportunity for political manipulation".

Hayashi, though, said Lai was travelling in a private capacity and there was no change to Japan's policy on non-governmental working relations with Taiwan.

Public memorials for Abe, 67, are expected to be held at a later date.

His hawkish, nationalist views were divisive, and he weathered a series of scandals including allegations of cronyism, but he was lauded by others for his economic strategy and efforts to put Japan firmly on the world stage.