Twenty-seven prisoners have escaped from a jail in the Brazilian city of Rio de Janeiro. The inmates fled through the prison's sewage system, BBC News reported.

Prison officials say they have already re-captured four of the escapees, and are confident none of the others has so far been able to leave the sewer tunnels.

Police are questioning the guards who were on duty at the Vicente Piragibe prison when the escape happened.

The recaptured escapees will also be questioned before being transferred to another penitentiary. Overcrowding is a major problem in many of Brazil's prison.

Local media quoted one unnamed prison official saying that Vicente Piragibe housed about 1,700 inmates and sometimes only had 10 prison guards on duty.