SORSOGON CITY. The four-kilometer radius around Bulusan remains off limits as the Philippine Institute of Volcanology and Seismology (Phivolcs) on Saturday maintained the alert level 2 in the areas surrounding one of the country's most active volcano.

The continued ash explosions overnight raised fears of a possible eruption and has caused the death of one man due to asthma attack, officials said.

Areas affected by the most recent explosion were the villages of Escuala and Purog in Casiguran town and San Isidro, Sta. Barabara, Buhang, and Purog in Bulusan, Sorsogon.

The ash explosion that occurred after midnight last night was the sixth this year.

Abner Ete of the observatory station in Sorsogon said Phivolcs personnel have been sent to the area to check on the extent of the explosion.

Phivolcs said an explosion from the 1,565-meter (5,134-foot) summit of Bulusan sent ash and steam one kilometer (3,300 feet) into the air and showered ash on surrounding villages in Sorsogon province in the Bicol region.

A 57-year-old local man died of asthma triggered by ash that has been spewing from the volcano since Wednesday, the civil defense office said.

The government earlier declared the town of Casiguran, on the slope of the mountain, a "calamity" area after ash from the volcano rained down on roofs.

The exact number of houses damaged in the disaster zone, on the southern tip of the main island of Luzon, was not disclosed.

There were no immediate plans to evacuate residents living around the volcano but the institute warned that there was an "increasing frequency in ash emissions," adding that more explosions were expected.

The institute reiterated that residents must stay at least four kilometers (2.5 miles) away from the crater, warning that volcanic deposits on the slopes of the mountain could turn into "life-threatening volcanic flows."

Bulusan has had 15 recorded eruptions, the latest in November 1994.

Twenty-two volcanoes are considered active in the Philippines, part of the so-called "Pacific ring of fire" made up of islands created by volcanic activity on the Western Pacific.