General Santos, Philippines. Rescuers searched ruined buildings in the southern Philippines on Tuesday to ensure no one was still trapped a day after one of the strongest earthquakes to hit the country in half a century killed at least 37 people and displaced more than 32,000.

Only four people were considered missing on official records in the southern provinces near where the 7.8 magnitude quake struck Monday morning, but the Office of Civil Defense acknowledged several collapsed and heavily damaged buildings must be thoroughly inspected for possible survivors or casualties.

The earthquake centered off Mindanao, the second most populous Philippine island, injured nearly 500 people and displaced more than 32,000, most of whom fled to emergency shelters.

Many people who left their homes feared a tsunami. Waves up to 1.4 meters (4.6 feet) above tide level were measured in the Philippines, but the only tsunami damage reported was to six shanties on stilts in a coastal village. Smaller waves washed ashore in Indonesia and Palau, and as far away as southern Japan.

Landslides and Building Collapses Caused Several Deaths
The earthquake left a trail of destruction, including in General Santos, a lively coastal city of more than 700,000 people known as the country’s tuna capital, where at least 13 people were killed in collapsed buildings and due to falling debris.

At least 18 died in Sarangani province, mostly in a landslide that buried houses in the mountainside town of Glan, according to Rafaelito Alejandro of the Office of Civil Defense.

The other deaths were reported in the southern provinces of South Cotabato and Davao Occidental, and on Balut Island, disaster response officials said.

About 2,500 houses and 117 government buildings and facilities were damaged in several provinces, according to an initial government damage assessment. The international airport in General Santos remained shut for a second day, forcing the cancellation of 63 domestic flights except for those on humanitarian missions.

About 6,000 public school buildings in quake-hit provinces must be assessed before classes can resume. The quake struck on the first day of classes nationwide after a two-month summer break, and many who sustained injuries were young students who had gathered with excitement for morning flag-raising ceremonies.

Authorities have warned that buildings that sustained cracks could collapse due to aftershocks, some of them dangerously powerful.

“We cannot force the immediate reopening of schools because we have to ensure the integrity of the buildings,” Alejandro said.

Strongest Quake Since 1976
Monday's earthquake was centered at sea at a depth of 33 kilometers (20 miles), about 32 kilometers (20 miles) southwest of Maasim town in Sarangani province.

It was set off by movement in the Cotabato Trench and was the strongest since the same undersea depression triggered an 8.1-magnitude quake that whipped up tsunami waves on Aug. 17, 1976, said Teresito Bacolcol, the director of the Philippine Institute of Volcanology and Seismology.

About 8,000 people died from that quake and tsunami waves of up to 8 to 10 meters (26 to 33 feet) that engulfed several towns and provinces, Bacolcol said.

The Philippine seismological institute was scheduled to commemorate the anniversary of the 1976 quake and tsunami in August by installing markers to remind vulnerable towns and cities of the need for constant vigilance, Bacolcol told The Associated Press.

A 1990 earthquake that also had a magnitude of 7.8 left more than 1,000 people dead, injured thousands, and caused extensive damage in northern provinces and cities.

President Ferdinand Marcos Jr. deployed top defense-mitigation officials from Manila to help oversee search and rescue, the distribution of tens of thousands of food packs and construction materials to quake victims, and assess damage to bridges, roads, and other infrastructure.

The United States, a treaty ally of the Philippines, said it was coordinating with Manila and was ready to support Philippine response efforts. France, Japan, and New Zealand also expressed support.

The Philippines 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 battered by about 20 typhoons and tropical storms each year, making it one of the world’s most disaster-prone countries.