Philippine authorities have started evacuating about 50,000 people from around the country's most active volcano as it spewed burning mud and rocks.

Mayon volcano, famed for its near-perfect cone shape in a coconut-growing region of the central Philippines, started to release lava early this week and vulcanologists are expecting a major eruption in the next few days.

"We are in the process of evacuating nearly 10,000 families around the 6-8 kilometre danger zone around the volcano," Cedric Daep, head of Albay province's public safety office, told reporters.

Mr Daep said the fleeing residents were being temporarily housed in school buildings and public gymnasiums, where local government officials set up food and relief centres.

"We have enough food for all these people for only a month," Mr Daep said, adding humanitarian and non-government groups have pledged to send food, water, medicines and blankets.

Renato Solidum, the country's chief vulcanologist, said the alert level around Mayon had been raised to number three, indicating volcanic materials were now near the top of the crater and "incandescent materials" were detaching.

Level four means an eruption is imminent while level five means an eruption is in progress.

"We've been monitoring a high-level of unrest and there could be a hazardous explosion coming," Mr Solidum said.

The Philippines lies on the Ring of Fire, a belt of volcanoes circling the Pacific Ocean that is also prone to earthquakes.

The last time Mayon erupted was in 2006.

- Reuters