Alert level 2 signifies increasing unrest due to low to moderate volcanic quakes, episodes of harmonic tremors and increase in sulfur gas emissions, said Eduardo Laguerta, resident volcanologist of the Philippine Institute of Volcanology and Seismology (Phivolcs).
Laguerta said the faint crater glow, observed since Wednesday night, was a "persistent and sizable phenomenon" and not a remnant of Mayon’s eruption two years ago.
Laguerta said a team from the Phivolcs central office has arrived here to set up a global positioning system some 700 meters southwest of the volcano as well as additional seismic sensors in the vicinity of Barangay Buang.
In July 2001, Mayon spewed ash. Last March 17, Phivolcs raised alert level 1 after the volcano again spewed ash.
Phivolcs warned the public from venturing into the six-kilometer permanent danger zone, especially in the southwest due to possible volcanic flows.