An alert bystander found the box containing the bomb in the vicinity of the Surigao City High School, and immediately notified the police.
The bomb was set to explode between 9 and 10:30 a.m. just when the students would go outside the school premises for recess, said Natz Corbeta, an officer of the Philippine Information Agency here.
"Fortunately, it was detected earlier and was detonated," Corbeta said.
Bomb expert PO3 Richard Charvit said the bomb had a blasting cap and was stuffed with nails and pieces of metal. Police detonated it using a water disruptor.
"We should be thankful to the informant who called us up. Had it not been for his call, it could have been a disaster," Surigao del Norte police director Ricky Nerbez said.
Meanwhile, two public elementary schools here received bomb threats moments after the Surigao City High School incident.
City education officials were forced to suspend classes in all public and private schools because of the bomb scare.
Surigao del Norte Gov. Robert Lyndon Barbers and Surigao City Mayor Alfonso Casuna advised the public to be always vigilant and, if possible, stay away from crowded areas.