At least three people were killed and four injured after a 7.8-magnitude earthquake shook southern Philippines early on Monday.The earthquake caused significant damage in the key coastal city of General Santos, knocked out power and sparked a tsunami alert along some regional coastlines. The city of over 700,000 people is a commercial hub on the island of Mindanao known for its tuna processing industry. The epicentre was 13km southwest of General Santos and had a depth of 10km, according to the Philippine Institute of Volcanology and Seismology. It struck at 7.37am local time.The Pacific Tsunami Warning Centre said waves up to 3m were possible along some coasts of the Philippines while waves up to 1m were possible on some coasts of Indonesia and Malaysia. Smaller sea changes were possible in Taiwan, Japan, Guam, Papua New Guinea, and several island nations and territories in the western Pacific. Teresito Bacolcol, head of the seismology institute, advised people living in coastal areas “to evacuate to higher grounds or go further inland”. The DZRH radio station in Manila reported a commercial building housing its provincial branch partly collapsed and staffers dashed to the ground floor without injuries. It wasn't clear if other people were trapped in the rubble of the four-story office building due to the earthquake, which struck before office hours.Tremors were felt as far as northcentral Indonesia and tsunami waves up to 18cm were recorded on some coasts of North Sulawesi and North Maluku provinces. The Philippines, one of the world’s most disaster-prone countries, is often hit by earthquakes and volcanic eruptions due to its location on the Pacific “Ring of Fire”, an arc of seismic faults around the ocean. The archipelago is also lashed by about 20 typhoons and tropical storms each year.