He was unconscious and a police officer who tried to extinguish the fire was also injured and both were transferred to a hospital, according to the report.
Abe was assassinated on July 8 and his state funeral is set for Sept. 27, with some 6,000 people from Japan and overseas set to take part.
But opposition to the event has been growing steadily because of revelations after Abe's killing of links between the ruling Liberal Democratic Party and the controversial Unification Church. The suspect in Abe's death said the church had bankrupted his mother and he felt the former prime minister supported it.
A majority of Japanese now oppose the funeral, with protests planned in the run-up to the ceremony and on the day it will be held, and this has sent current Prime Minister Fumio Kishida's support plunging.
(Reporting by Mariko Katsumura, Kaori Kaneko and Elaine Lies; Editing by Christian Schmollinger)
