MANILA, June 11 (AFP) - Thousands of people living near a Philippine volcano have taken shelter in evacuation centres as officials warned Sunday of health risks from ash and toxic gases spewing from the rumbling crater.

Seismology researchers said they had recorded at least one volcanic earthquake in the past 24 hours and red-hot rocks were falling from Mount Mayon in the central province of Albay.

More than 12,800 people have been moved to evacuation centres, the Philippine civil defence office said, most from farming villages at or near the foot of the volcano.

"There is a concomitant health risk while being close to the eruption because of inhaling sulphur dioxide gas or the particulate matter of ashfalls," Health Secretary Teodoro Herbosa told a press briefing Sunday.

Mayon, about 330 kilometres (205 miles) southeast of the capital Manila, is considered one of the most volatile of the country's 24 active volcanoes.

The Philippine Institute of Volcanology and Seismology said rocks were falling from a disintegrating lava dome being pushed out of the crater by molten material below the earth.

The rocks were raining down on areas up to two kilometres away and sulphur dioxide emissions had tripled on Saturday, state volcanologists said.

A five-step alert system for the volcano was raised from two to three on Thursday, with authorities warning of possible respiratory illnesses from inhaling fumes.

"With Albay in a state of calamity due to Mayon's activity, we remind people to follow the recommendations and evacuation instructions of your local governments," Philippine President Ferdinand Marcos said Saturday.

Earthquakes and volcanic activity are common in the Philippines due to its position on the Pacific "Ring of Fire" where tectonic plates collide.

Five years ago, Mayon displaced tens of thousands of people after spewing millions of tonnes of ash, rocks and lava.

The country's most powerful eruption in recent decades was Mount Pinatubo in 1991 that killed more than 800 people.

That disaster produced an ash cloud that travelled thousands of kilometres.