LEGAZPI CITY, Philippines—-Sulfur dioxide emission and quakes showed clear signs that Mayon volcano continues to be on a heightened state of restiveness, said the Philippine Institute of Volcanology and Seismology on Monday.

A Phivolcs bulletin on Monday said the volcano released 853 tons of sulfur dioxide during the past 24 hours, a reading which was way above the 505 tons a day recorded on Sunday.

The sulfur dioxide disgorge from Mt. Mayon indicated a fluctuating trend ranging from 350 to 853 tons per day.

There were 505 tons per day recorded on Oct. 10; 761 tons on Oct.8; and 350 tons on Oct. 7.

Ed Laguerta, Phivolcs resident volcanologist, said that “350 tons per day to 853 tons per day during the past five days is an indication that magma is intruding into the volcano’s vent.”

The agency's seismic instruments detected 7 volcanic earthquakes which brought about a total of 43 quakes recorded during the past five days or a total of 106 earthquakes rocking the volcano since October 1.

High and low frequency harmonic quakes detected by the instruments signified that magma intrusion is developing in the volcano’s crater vent.

Laguerta said the agency is still assessing the abnormal state of the volcano based on other given parameters like ground deformation and crater glow.

In its latest bulletin, Phivolcs said the volcano did not exhibit crater glow due to cloudy sky prevailing in the volcano’s crater.

Alert level 2 remains hoisted over Mayon with Phivolcs strongly recommending that the 6-kilometer Permanent Danger Zone, including the 7-km extended danger zones in the southeast flank, be off limits to any human activity due to threats from sudden explosions and rockfalls from the volcano's upper slopes.

In August scientists kept watch for a feared collapse of a portion of Mayon’s crater, which holds an estimated 200,000 cubic feet of rocks.

Mayon Volcano, famous for its nearly perfect conical shape, has a height of over 2,400 meters.

The volcano, said to be the most active in the country, has erupted at least 50 times since 1616. Its worst eruption buried Cagsawa town and killed 1,200 people in 1814. An eruption in 1993 killed more than 70 farmers.

Mayon erupted again in 2006.