Typhoon Mitag was packing 120 kilometer (75 mile) per hour winds with gusts of up to 150 kph (94 mph) as it blew westward from the Philippine Sea at 15 kph (9 mph) toward the Bicol region at midday, chief government forecaster Nathaniel Cruz said.
It could be a "super typhoon" with winds of over 220 kph (138 mph) when it makes landfall at the weekend, he said.
Disaster officials said about 800 families, or 4,000 people, already have moved to temporary shelters in four towns in Albay province and one town in nearby Sorsogon.
President Gloria Macapagal Arroyo, worried about a repeat of last year's disaster, has ordered mass evacuations in the typhoon's expected path and cut short her trip to Singapore , where she was attending an Asian summit.
Cruz said if the typhoon doesn't change direction, it will hit Bicol by Saturday morning or veer northwest and make landfall in Quezon province farther north the next day.
The typhoon is also enhancing northeast monsoon rains, drenching the eastern Philippines, he said.
Albay Gov. Joey Salceda has suspended classes so some schools can be used as temporary shelters.
Cedric Daep, executive officer of the provincial disaster office, said full evacuation of the most threatened communities along the coastline and in the foothills of the Mayon volcano will begin Thursday afternoon.
"It's been raining for many days in some areas, and these are ripe for landslides," said Glenn Rabonza, administrator of the Office of Civil Defense.
He warned that storm surges from a powerful typhoon could generate waves 3-10 meters (10-30 feet) high that could wreak havoc on coastal villages.
Officials estimate up to 200,000 people may have to be evacuated in Albay, which last year bore the brunt of Typhoon Durian that triggered flash floods and unleashed tons of volcanic debris, wiping out entire communities and killing more than 1,000 people. About the same number of people died in 2004 in Quezon when it was hit by successive storms and typhoons.