LEGASPI, Philippines (Reuters) - The Philippines raised the alert level around the country’s most active volcano on Sunday, warning of a possible hazardous eruption within days and extending a “no-go zone” up to 10 km (6 miles).

Lava continues to cascade further down the slopes of Mayon volcano in Legaspi city, about 500 km (311 miles) south of Manila, December 20, 2009. REUTERS/Stringer

Mayon Volcano, known for its near-perfect cone shape in the coconut-growing central Bicol region, has been spewing ash and burning mud and rocks since Monday, chief vulcanologist Renato Solidum said.

“We raised the alert level to 4 ... meaning an eruption is within days,” Solidum told Reuters after aerial inspection and other observations of the volcano showed increased activity in the past 24 hours.

Level 4 indicates an eruption is imminent and the maximum alert level of 5 means an eruption is underway, he said.

Solidum said more than 450 volcanic tremors were monitored in the past 12 hours and rumbling sounds had been heard at the base of the volcano.

More than 40,000 people -- about 85 percent of the population in the area -- have already been moved to temporary shelters, where food and water stations have been set up. About 50,000 masks were distributed on Sunday to displaced people.

Joey Salceda, governor of Albay province where Mayon is located, said he had ordered the deployment of more troops around the expanded no-go zone to forcibly evacuate more people and to stop others who wanted to return to their homes and farms.

“We’re preparing to evacuate more people before the actual big eruption,” Salceda told reporters.

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

Mayon is the most active of 22 volcanoes in the country, having erupted more than 50 times in the past four centuries. The most destructive eruption was in February 1841, when lava flows buried a town and killed 1,200 people.

The last time Mayon erupted was in 2006.