© REUTERS/Willy KurniawanIndonesian police officers stand guard following a blast at National Monument (Monas) complex in Jakarta, Indonesia, December 3, 2019.
A video has emerged on social media showing a man, his face and clothes covered in blood, lying motionless on the ground before slowly sitting up.
Two people were injured in the blast, local media reported. Both of them were taken to the hospital for treatment.
The site of the explosion, Indonesia's National Park - commonly referred to as Monas park - is located in front of the presidential palace, where military servicemen were reportedly performing an exercise at the time of the blast.
While the investigation is still in its early stages, authorities believe the blast was caused by a smoke grenade. It's unclear whether this was an accident or if foul play was involved. The site of the incident has been sealed off by military and police, and the adjacent area has been closed to public.
"We haven't concluded so, because we're still investigating," Jakarta military chief Eko Margiyono said, as cited by Reuters, when asked if the authorities would treat the incident as a targeted attack on military personal.
Indonesian President Joko Widodo was not at his residence at the time of the attack, his spokesman said.
While no group has claimed responsibility for the incident, Indonesia has lately seen a spike in home-grown Islamist-linked violence. On November 13, a suicide bomber denoted an explosive device at a police station in the city of Medan, injuring six people.
Comment: See also: Indonesian society splinters under conservative draft laws