More than 3,000 prisoners are believed to have escaped from the main prison in Democratic Republic of Congo, security sources have told the BBC.
The authorities say only around 50 prisoners got away when armed men attacked the prison on Wednesday.
The security sources also said dozens of people were killed during the attack on Makala prison.
Ne Muanda Nsemi, leader of the political-religious sect Bundu Dia Kongo, is among those who escaped.
A police spokesperson told a local radio station, Radio Okapi, that the prisoners were dangerous, and called for anyone who saw them to tell the authorities.
The sources say that around half of the prison’s inmates fled during the attack.
Government officials say a police officer and at least five attackers were killed, while several sources say that up to 100 died.
The authorities accuse supporters of Mr Nsemi’s supporters of being behind the attack, although the group has denied this.
Mr Nsemi is a self-styled prophet seeking to revive the ancient Kongo kingdom.
Bundu Dia Kongo is campaigning to restore a monarchy in parts of DR Congo, Congo-Brazzaville, Angola and Gabon.
The group mixes Christian and traditional beliefs and practices.
Mr Nsemi was an MP when he was arrested in Kinshasa after police accused him of inciting violence.
Ne Muanda Nsemi: The man behind the unrest
Former chemistry professor at the University of Kinshasa
- Comes from the minority Bakongo ethnic group
- Claims to have received a revelation from the “Archangel of the Kongo” in 1969
- Formed the Bundu dia Kongo (BDK) movement in 1986
- Wants to re-establish the Kongo kingdom that once straddled four modern-day states.
- Supporters and security forces involved in violent clashes
- Elected to parliament in 2006 as an independent
- Formed the Bundu dia Mayala political party in 2010 after BDK banned
- Arrested in March after security forces besiege his home for two weeks
- Escapes from jail on 17 May