The Pinatubo Volcano was placed on Alert Level 1, the lowest warning, after 1,772 imperceptible earthquakes beneath the surface were recorded, Phivolcs said.
The alert indocates "low level unrest" that could be attributed to "tectonic processes" or movement's in the Earth's crust, Phivolcs said.
However, "no imminent eruption is foreseen," Phivolcs said.
Entry into the Pinatubo Crater area must be made with "extreme caution and should be avoided if possible," it said.
NEWS YOU CAN USE: What Do Volcano, Typhoon Alerts Mean?
Mt Pinatubo erupted in 1991 after centuries of dormancy. The USGS called it the largest volcanic eruption in the last 100 years. The amount of ash it spewed into the atmosphere caused global temperatures to drop slightly.
Taal Volcano, where earthquakes had been recorded in higher frequencies, stays under Alert Level 1, Phivolcs said.
