Long lines of mourners formed outside central Tokyo's Zojoji temple, the site of Abe's funeral, by early morning on Tuesday.
The 1pm (2pm AEST) ceremony is open only to family and close friends.
Hundreds of mourners had filed into the temple in steamy summer heat on Monday evening to pay their respects to Abe, who died aged 67.
His killing on Friday by a man wielding a homemade gun stunned a nation where both gun crime and political violence are extremely rare.
Following the funeral, the hearse bearing Abe's body will proceed through downtown Tokyo, where black mourning ribbons draped Japanese flags.
The procession will take in the capital's political heart of Nagatacho, including landmarks such as the parliament building Abe first entered as a young MP in 1993, and the office from which he led the nation in two stints as prime minister, most recently from 2012 to 2020.
Tributes have poured in from international leaders, with Australia's Prime Minister Anthony Albanese saying on Monday: ""The friendship the former Japanese prime minister offered Australia was warm in sentiment and profound in consequence".
US Secretary of State Antony Blinken making a brief, unscheduled stop on Monday morning to pay his respects.
French leader Emmanuel Macron sent his condolences in footage posted on the country's official presidential Twitter account after he visited the Japanese embassy in Paris.
"I remember all our meetings and work together, especially during my visit (to Japan) in 2019 ... I've lost a friend," Macron said.
"He served his country with great courage, and audacity."
The suspected killer, arrested at the scene and identified by police as 41-year-old Tetsuya Yamagami, believed Abe had promoted a religious group to which his mother made a "huge donation", Kyodo news agency has said, citing investigators.
The Unification Church, known for its mass weddings and devoted following, said on Monday the suspect's mother was one of its members.
Reuters could not determine whether the mother belonged to any other religious organisations.
