LEGAZPI, Philippines — Almost all of the 47,000 residents living on the slopes of a rumbling volcano in the central Philippines moved to emergency shelters, and lava and earthquakes today heralded what officials say could be a major eruption.

Low clouds obscured visibility of the smoldering 8,070-foot Mayon, towering over coconut farms and rice paddies in coastal Albay province.

"Hazardous eruption ... can happen today or in the next few days," said chief state volcanologist Renato Solidum, adding an eruption also might not happen.

Ash columns were seen rising during a cloud break, and Solidum said his team recorded 1,266 volcanic quakes in the last 24 hours, down from nearly 2,000 the previous day. He said while the quakes were fewer, they were larger.

The emission of sulfur dioxide — an indication of magma rising inside the volcano — was measured at 6,530 tons per day, slightly less than 7,000 tons Sunday, but still very high, Solidum said. The normal gas emission is 500 tons per day.

"Technically, Mayon volcano is already erupting because lava has oozed out," said Mahar Lagmay, professor of geological studies at the University of the Philippines.