At least 40 prisoners escaped using a tunnel dug 10 meters deep under the wall of a police station in Curitiba, south Brazil.

According to reports, dozens of prisoners awaiting trial in the São Jose dos Pinhais station fled through the tunnel in the early hours of Monday morning. The break-out happened under the watch of three policemen, who said that they were unaware of what was happening.

Some 17 prisoners have already been recaptured.

This is not the first escape of prisoners from the São Jose dos Pinhais police station. In 2010, 30 people escaped through a hole in the station’s roof. The unit was highly overcrowded, holding 146 prisoners despite being built for 36.

As InSight Crime has noted, Brazil’s entire penal system is overburdened, with facilities unable to keep up with the number of arrests.

The escape comes just weeks after more than 70 inmates escaped by overpowering guards at a prison in the state of Santa Catarina, southern Brazil.