A vote counting machine (VCM) and a ballot box were set ablaze in San Pablo town in Zamboanga del Sur on Wednesday night.
A grenade was also lobbed outside the local fire substation in Purok Purol Maloloy-on in Barangay Poblacion allegedly to prevent firemen from responding to the fire.
The substation is near the San Pablo Central Elementary School where at least eight ballot boxes and VCMs were kept inside the Grade 6 classrooms while SD cards have yet to be transmitted for canvassing.
Canvassing in the area was on recess pending transmittal of the SD cards.
The fire totally burned a VCM and a ballot box containing 340 ballots.
Municipal Election Officer Ian Tria said authorities were able to save 7 other sets of VCMs and ballot boxes from the fire.
No one was hurt in the incident.
On Tuesday morning, armed men set fire to a VCM in Jones, Isabela province while it was being delivered to the municipal hall on board a dump truck.