Twenty-eight inmates escaped from a Belgian prison early on Saturday after overpowering guards.
Some say the break-out was the biggest in Belgian history
Six were swiftly recaptured, but police have launched an extensive search operation for the others.
Two prisoners managed to force their cell door open and took several guards hostage, demanding their keys, local officials said.
The two then freed 26 others at Dendermonde jail, north-west of Brussels. No-one was hurt.
The escaped prisoners managed to get into the prison courtyard and succeeded in scaling the prison walls.
The authorities were unable to say how the cell door had been forced or whether any dangerous criminals had managed to escape.