More than 250 inmates have escaped from Bukavu prison, on the border between Congo and Rwanda.
The inmates managed to force their way through the main gate following an exchange of gunfire on Thursday afternoon, AFP news agency reported.
"We have just finished the tally, there were a total of 301 escapees, but 35 have already been recaptured," a police officer, who spoke under condition of anonymity, said.
"The provisional toll this afternoon is two dead, a civilian and a soldier, and seven injured including three civilians and four soldiers."
The officer explained that prison wardens had been overcome by the inmates, who "took weapons and managed to open the prison door."
Descartes Mponge, president of the South Kivu Civil Society organisation, told AFP there were "at least 1,600 prisoners in this prison" at the time of the breakout.
Large numbers of police and soldiers surrounded the prison after the escape.
The BBC's DR Congo correspondent Maud Jullien said jailbreaks are fairly common in DR Congo, where at least 240 prisoners escaped in another eastern town less than a year ago.
Nearly 1,000 prisoners escaped from a prison in eastern DR Congo in 2011.