LEGAZPI CITY, Philippines—Mayon Volcano released 1,272 tons of sulfur dioxide during a 24-hour period between Tuesday and Wednesday morning that was way above the fluctuation range recorded in previous weeks, the Philippine Institute of Volcanology and Seismology (Phivolcs) said Thursday

The emission was the highest during the last two-month observation period, a Phivolcs bulletin said, adding it was not able to record the gas level during the Wednesday-Thursday monitoring period due to bad weather.

The gas emission and other signs of abnormality shown by the volcano prompted disaster authorities to strictly enforce a ban on people entering designated danger zones around the volcano. Police and military personnel manned 12 checkpoints intended to ensure no one ventured into the "no-man’s land" in the municipalities of Camalig, Daraga, and Sto. Domingo, and the cities of Ligao, Tabaco and Legazpi.

Colonel Marlou Salazar, commander of the Army's 901st Infantry Brigade, said earlier that the Task Force Mayon had prepositioned military trucks in case an evacuation order is given by Governor Joey Salceda, Provincial Disaster Coordinating Council chair, in the event Philvolcs raised the alert to Level 3.

Gas emission trends from Mayon's crater showed a high level of unrest with 971 tons per day on October 12, 853 tons on October 11, and 505 tons on October 10, all were above the baseline data of 500 tons per day.

Thursday's bulletin also revealed an increase in the number of volcanic earthquakes by 11. It said there were 17 quakes during the past 24-hour period, compared to the six quakes in the previous monitoring period, bringing the total to 73 quakes recorded since October 5.

Scientists said the volcano's abnormality levels were an indication of a possible eruption.

They were continuously monitoring tremors, gas emissions and ground deformation as these are indications that the volcano's seismic activity may intensify.

Grater glow was not visible as the volcano was covered by clouds.

Alert Level 2 remains hoisted over the volcano and Phivolcs strongly recommended that the six-kilometer permanent danger zone and the seven-kilometer extended danger zone continue to be off-limits due to the threat from sudden explosions and rockfalls from the upper slopes of the volcano.

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.