A blast outside the headquarters of San Miguel Corp
Police cordoned off the area after the pre-dawn blast, but employees were allowed in when they arrived for work. The company's large sign outside the building was damaged and lights were shattered.
Bomb experts were examining fragments of the explosive substance for clues but there was no immediate word on who may have ben responsible.
"It is too early to speculate on the motive behind the attack. We are still investigating," the city's eastern police district head Chief Superintendent Benjardi Mantele told reporters.
San Miguel, which is moving into infrastructure and heavy industry after diversifying from its core food and drinks business, is locked in a dispute with environmental activists and tribesmen over the building of a dam in the eastern province of Rizal.
The protesters were planning a march to the San Miguel office on Monday to protest the building of the dam.
Blast shatters lights at San Miguel HQ in Philippines
A blast outside the headquarters of San Miguel Corp <SMC.PS> <SMCB.PS> in the Philippine capital early on Monday caused minor damage but no one was injured, police said, Reuters reported.
