More than 3,000 villagers remaining in a no-go zone around the Philippines' rumbling Mayon volcano have started evacuating the area after officials threatened to force them out. Scientists have warned that powerful booms emanating from the country's most active volcano, located about 330 kilometres south-east of Manila, indicate that a major eruption is imminent. <br/><br/>The Philippine Institute of Volcanology and Seismology says seismic activity has increased in number and size. It says a total of 1,942 volcanic quakes have been detected since Sunday, while sulphur dioxide emissions are very high. Nearly 44,400 people have already taken shelter in the evacuation centres since Mayon started belching ash, steam and lava last week. Authorities said if the alert level is raised to five, another 16,000 villagers living beyond the danger zone would also have to be evacuated as a precautionary measure.<br/>