MANILA — An offshore magnitude 7.8 earthquake rocked the southern Philippines Monday, killing at least 32 people, according to provincial authorities, after toppling buildings and sending a 1-meter tsunami into nearby coasts.

National disaster authorities said at least a dozen people were still missing, while more than 200 others had sustained injuries. Thousands of villagers were displaced, Office of Civil Defense spokesperson Junie Castillo said.

The quake came early in the morning as schools were reopening in the Philippines after a long break, with the tremors felt strongly in a dozen provinces and 420 kilometers away in the city of Manado on the Indonesian island of Sulawesi.

A few buildings collapsed and key infrastructure sustained quake damage in the hard-hit city of General Santos, a port city of about 720,000 people.

The quake also triggered a landslide in Glan, Sarangani Province, that killed 13 villagers.

It was the strongest quake to strike the Philippines this year, and was centered at sea off Mindanao, the second-most populous island in the Philippines, said Teresito Bacolcol, the director of the Philippine Institute of Volcanology and Seismology.

The Philippine seismology agency said at least nine strong aftershocks were felt across Mindanao on Monday morning, the strongest at a 6.7 magnitude.

Philippine President Ferdinand Marcos Jr ordered the cancellation of classes and directed disaster-response agencies to immediately get to work in quake-hit provinces, saying "the national government is moving and we will not leave Mindanao behind".

The Philippine military said its disaster response units had been deployed to affected areas and the full extent of the damage was not yet clear and authorities said assessments were underway.

Tsunami warnings

Tsunami damage was reported in at least one coastal village and a tsunami with a wave height up to 0.75 meters was detected in some regions of North Sulawesi.

Tsunami alerts were issued in the southern Philippines, northern Indonesia and the Malaysian state of Sabah on Borneo Island after the quake.

The US Tsunami Warning System said multiple countries could be affected and Australia initially warned of potential tsunami waves on its northern coasts. Japan's meteorological agency issued an advisory and said a tsunami of 0.2 meters or lower had been observed, with some disruption to ferries and precautionary beach closures.

The international airport in General Santos was temporarily shut, and 17 domestic flights were canceled, the Civil Aviation Authority of the Philippines said.

The earthquake comes eight months after the Philippines suffered its deadliest tremor in 12 years, when a shallow 6.9 magnitude quake hit off the island of Cebu, killing 79 people. Two powerful quakes struck Mindanao two weeks later, the strongest at a magnitude 7.4.

AGENCIES VIA XINHUA