Chief Superintendent Eliseo de la Paz, Eastern Visayas police director, said the police have launched a manhunt for the fugitives.
"My order is to shoot them on sight once they resist arrest," said De la Paz, describing the 11 escapees as armed and dangerous.
He said an initial investigation showed that one of the inmates was armed with a smuggled gun and shot a jail guard.
Other guards rushed in after hearing the gunfire, but were overpowered by the other inmates.
A second guard was killed and two others were wounded in the ensuing melee before the prisoners escaped, De la Paz said.
The slain guards were identified as Isagani Luis and Edwin Miranda. Seriously wounded were Dennis Tonog and Edgar Poño.
De la Paz said the provincial jail houses more than 200 inmates, locked up in single cells.
The escapees were led by a suspected communist rebel hit man, Jessie Galecio, whom De la Paz described as "a known escape artist" who had twice bolted jail before being recaptured.
The other inmates were facing murder and homicide charges, he said. They were identified as Allen Banquillo, Gilbert Jackson, Arnold Joropojop, Valentin Mendez, brothers Jose and Rizal Paet, Joan Magsaysay, Roan Rovilles, Brigido Mendez, and Roy Rosila.
"Right now, we are trying to find out how the caliber .45 pistol ended up in the hands of the prisoners without being detected by the jail officers. This is obviously negligence on their part," he said.
Northern Samar Gov. Raul Daza has ordered retired Col. Alberto Mendador, the provincial jail warden, to thoroughly investigate the incident and take the necessary action against jail personnel found negligent in their duties.
Police said it was the 17th jailbreak in the country this year, and that a total of 76 inmates had escaped. Last year, police reported 51 jailbreaks leading to the escape of 141 inmates.
The country’s prisons have a reputation for being some of the world’s most porous because of frequent jailbreaks blamed on dilapidated facilities, corrupt guards and harsh conditions. — Miriam Garcia Desacada, AP