Renato Solidum, chief of the Philippine Institute of Volcanology and Seismology (Phivolcs) said he would not order an immediate evacuation of the area surrounding the 2,474-meter (8,118-foot) volcano because a possible violent eruption could take weeks.

Meanwhile, some officials in this capital of Albay are looking into the possibility of luring tourists to watch the eruption. Already, residents of this city have watched in awe as lava flowed down the slope from the crater, stirring up brownish-grey clouds of volcanic dust in their wake.

“What is happening now is a mild and quiet type of eruption,” Solidum said. “What we are watching is the rate by which this magma is being extruded. If it is faster and stronger, it will lead to more hazardous eruptions."

Volcanologist Ed Laguerta said red-hot boulders, some the size of cars, broke into smaller pieces after being expelled from the crater, piling up about four kilometers (2.5 miles) down the southeastern slope.

Explosive eruptions could occur “as gas-rich lavas are expelled,” the volcanology institute warned. Solidum said earlier such an eruption may happen “within weeks.”

Mayon’s most violent eruption, in 1814, killed more than 1,200 people and buried an entire town in volcanic mud. An eruption in 1993 killed 79 people.

In the evening, one can see the two-kilometer long streak of lava slowly snaking its way down the southeastern slope, said Jukes Nunez, an operations officer with the provincial disaster officer.

Nunez said an eruption warning system already is in place for quick evacuation of nearby communities, and radio stations also will broadcast emergency calls.

“There is no more human activity” within the six to seven kilometer (3.75-4-mile) danger zone, Nunez said.

Cedric Daep, Albay provincial disaster action officer, said relief officials were stockpiling food and readying evacuation centers. Daep said groups have been formed to transport evacuees, provide security for abandoned communities, and provide health and sanitation services at the centers.

Mayon, one of the country’s 22 active volcanos, last came to life in a series of eruptions in 2001, forcing the evacuation of more than 60,000 people. It has erupted about 50 times since 1616.

In February, scientists closely monitored Mayon after low-frequency quakes and ash puffs indicated magma was rising in its crater.

Phivolcs recorded 147 low-frequency volcanic earthquakes over a 1.5-hour period, compared with five or fewer during quiet times.

“These low-frequency volcanic earthquakes were relatively large and are interpreted to be caused by the shallow movement of magma within the summit crater," a bulletin issued by the institute said.

The volcano has been restless since October 2004, when officials raised the second of a five-level alert system, indicating “increasing unrest,” and warned villagers to stay out of a permanent 6-kilometer (3.75-mile) danger zone.

The Philippines is in the Pacific “Ring of Fire,” where volcanic activity and earthquakes are common. Bulusan volcano, about 50 kilometers (31 miles) south of Mayon, has ejected ash in about five minor explosions since March.

Last month, Phivolcs were closely monitoring Bulusan Volcano in nearby Sorsogon province after alert level was raised to 2 (probable eruptions in months or weeks).

In June 1991, Mount Pinatubo exploded in the northern Philippines in one of the world’s biggest volcanic eruptions of the 20th century, killing about 800 people.