LEGAZPI, Philippines, Dec 18, 2009 (AFP) - Farmers have begun returning to the foothills of the Philippines' most active volcano despite an increasing flow of lava from the mountain, officials said Friday.

The picturesque Mayon volcano continued to spout spectacular fountains of ash into the sky amid a series of minor eruptions, heightening concerns that a major explosion could occur at any time.

Earthquakes inside Mayon also increased due to the enormous pressure of the ever-increasing amount of lava on its slopes, according to the government's volcanology institute.

"The important thing is that people should not be in those danger zones when a hazardous explosion happens," said chief government volcanologist Renato Solidum.

The so-called danger zone is a radius of six to eight kilometres (3.5 to five miles) from Mayon, and nearly 50,000 people have been evacuated from those areas since the volcano began spewing lava on Monday.

But the zone is a fertile vegetable farming area and many people from the evacuated villages have been creeping back to look after their crops and animals.

"There is nothing we can do except to keep taking them out when we find them in the danger zone," said Joey Salceda, governor of Albay province where Mayon is located.

The Philippine Institute of Volcanology and Seismology raised the alert level to three for Mayon on Monday.

Level three means an eruption is likely in the very near future. The scale runs from one to five, with five meaning a hazardous eruption is occurring.

Despite the increased activity on Friday, the volcanology institute said there was no need to raise the alert level to four.

Mayon, which is about 330 kilometres (200 miles) southeast of Manila, has erupted 48 times since records began, claiming thousands of lives.

However the 2,460-metre (8,070-feet) volcano remains a popular tourist attraction, and is particularly famous for its perfect cone.