By Elaine Lies

TOKYO, July 12 (Reuters) - Japan on Tuesday prepared to bid farewell to Shinzo Abe, a polarising figure who dominated Japanese politics for decades as the country's longest-serving premier, before being gunned down at a campaign rally last week.

Long lines of people dressed in black, mixed with others in informal clothing with backpacks, formed outside central Tokyo's Zojoji temple, the site of Abe's funeral, by early morning. The 1:00 p.m. (0400 GMT) ceremony itself 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 an unemployed 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 lawmaker in 1993, and the office from which he led the nation in two stints as prime minister, the longer from 2012 to 2020.

Tributes have poured in from international leaders, with U.S. Secretary of State Antony Blinken making a brief, unscheduled stop on Monday morning to pay his respects. U.S. Treasury Secretary Janet Yellen and Taiwan vice president William Lai, on a private visit as a family friend, also joined mourners.

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," said a solemn Macron.

"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. (Reporting by Elaine Lies; Editing by Kenneth Maxwell)