Japanese media claim that a man set himself on fire near the prime minister's Tokyo office in protest over plans to hold a state burial for former leader Shinzo Abe later this month.
TV Asahi reported the man set himself on fire early Wednesday and was hospitalised with burns. An injured police officer tried to put out the fire.
Kyodo news agency and other agencies reported a guy "engulfed in flames" about 7am (22:00GMT). A note criticising Abe's state funeral was nearby.
Police, the PM's office, and the cabinet office declined to comment.
Abe, Japan's longest-serving prime leader, was assassinated while campaigning on July 8. On September 27, 6,000 Japanese and foreigners will attend a state funeral in Tokyo.
The decision is contentious because state funerals are rare in Japan. More than half the public opposes the event, according to polls.
Growing discoveries about the LDP's ties to the Unification Church have fueled resistance. The murder suspect said the organisation bankrupted his mother and Abe backed it.
The Unification Church was founded in South Korea in the 1950s, and the LDP revealed last month that over half of its 379 legislators have interacted with a cult.