The alert level around Mayon volcano in the Philippines was raised from level three to level four on Sunday, meaning an explosive eruption could take place in days, government volcanologists said.

"We raised it to level four this afternoon because there was a sudden acceleration in the activity of the volcano," said July Sabit, head of the volcano monitoring team.

He said the number of volcanic quakes from 8:00 am (0000 GMT) Sunday increased to 463 and that the volcano was belching more sulphur dioxide into the air.

There were also rumbling sounds detected from inside the volcano, the volcanologists said.

This was a sign that "a hazardous eruption is possible within days."

However Sabit would not give an exact estimate of when the eruption could take place.

Just hours earlier, volcanologists said an eruption could occur in two weeks.

The government has already evacuated more than 8,600 of the 9,000 or so families living within an eight-kilometre (five mile) danger zone set up around Mayon, civil defence officials said.

"Those left behind are in the edges of the eight-kilometre zone. We are still convincing them to pull out," local civil defence head Raffy Alejandro said.

"We try to do the persuasive thing but if (it) gets bad, the governor has instructions to forcibly evacuate them," he added.