PORT-AU-PRINCE, Haiti - As many as 30 inmates escaped through a small hole in a prison wall in the latest of several breakouts from Haiti's largest penitentiary, police said Tuesday.

Witnesses told local media that prisoners waited for a police patrol to pass before slipping through a 20-inch hole and fleeing the overcrowded National Penitentiary during the day on Monday, just blocks from Haiti's National Palace.

Police quickly cordoned off the area and searched houses for the inmates. It wasn't immediately clear how many escaped, but officials said up to 30 prisoners may be missing.

Police Inspector General Fritz Jean told reporters the escape was under investigation. Private radio station Kiskeya reported that four prison guards were arrested on suspicion of involvement.

Police spokesman Frantz Lerebours declined to take questions when reached by phone, saying senior authorities were meeting to discuss the escape.

In July, 26 Haitian convicts deported from the United States escaped from a holding cell at the National Penitentiary.

In February 2005, nearly 500 prisoners escaped from the same prison in a jail break allegedly aided by corrupt guards who unlocked the doors and allowed inmates to flee.

A year earlier, hundreds of prisoners escaped amid the chaos of a revolt that toppled former president Jean Bertrand Aristide on Feb. 29, 2004.

The prison was built nearly 100 years ago to house 800 prisoners but reportedly holds twice that number, many of whom have languished in squalor for years while awaiting resolution of their cases.

When President Rene Preval took the oath of office in May, inmates rioted and gathered on the prison roof where they held aloft signs demanding their freedom.