MANILA (AFP) - Thirteen detainees facing drug charges escaped from jail on Sunday (Feb 26), the latest in a series of prison breaks in the Philippines, authorities said.

The 13 slipped out of the jail in a police camp in San Fernando city north of Manila before dawn, said Derrick Arnold Carreon, spokesman for the Philippine Drug Enforcement Agency.

"They sawed through the bars of the metal grille," he told AFP, adding an investigation was under way to find out how they got the saw.

The Philippines has frequently suffered mass escapes from prisons which are usually overcrowded, poorly maintained and inadequately guarded.

In the country's biggest jailbreak, more than 150 inmates ecaped a prison in the southern Philippines in January after about a hundred gunmen stormed the facility.

In August 2016 members of a Muslim extremist group that pledges allegiance to the Islamic State group stormed a jail in the south and broke out 23 inmates.