Gunfire was heard in several areas of the city from around 1:45 a.m., but the fighting appeared to have stopped by the afternoon, according to local residents and a Reuters witness.
“Thugs and uncivilized people disturbed the peace of our fellow citizens in some areas of the city of Bukavu,” South Kivu province’s governor Theo Kasi in a statement.
Security forces killed six gunmen and captured 36 others, while one member of the police and two soldiers were also killed, he said.
The city was last convulsed by fighting in November 2017, when the army clashed with troops loyal to a renegade general.
More than 120 rebel groups continue to operate across large swathes of eastern Congo since the official end of the civil wars in 2003.
Around 40 fighters entered the city from the north singing songs calling for the liberation the country, said Bob Kilubi, a local army commander.
“Some of them wanted to attack the military camp to loot the ammunition, the army prevented them,” Kilubi told Radio Maendeleo, a Bukavu-based radio station.
It remained unclear who was behind the attack. Kilubi blamed CPC64, a previously unknown armed group. One resident in the Bagira neighbourhood reported seeing a yellow flag with a red border flying from a tree, with the letters “ACN: Action for a New Congo”.
By Crispin Kyalangalilwa.
(Additional reporting by Justin Makangara, Fiston Mahamba and Hereward Holland; writing by Hereward Holland; Editing by Toby Chopra and Alex Richardson)