MANILA (AP): Scientists say the Philippines' most active volcano is rumbling again while emitting steam and a strong glow at the summit crater that can be seen with the naked eye.

State volcanologists say the frequency of volcanic earthquakes has increased on Mayon signifying the possible movement of magma below the surface that could lead to ash explosions and eventually eruption.

The 8,077-foot (2,462-meter) cone-shaped volcano in the central Bicol region spewed ash and lava from July to October 2006 sending about 30,000 people away from homes.

Typhoon-triggered mudslides along Mayon's slopes buried entire villages in December 2006 killing more than 1,000 people.

Authorities on Friday say they have raised a five-step alert system from 1 to 2.