A few buildings collapsed and key infrastructure sustained quake damage in the city of General Santos on Monday, and tsunami damage was reported in at least one coastal village.
Smaller waves were measured in Indonesia and Palau and as far away as southern Japan.
"It's a major earthquake and we're expecting damage," Teresito Bacolcol, the director of the Philippine Institute of Volcanology and Seismology, told The Associated Press.
The strongest quake to strike the Philippines in 2026 was centred at sea off Mindanao island at a depth of 33km, about 32km southwest of Maasim town in Sarangani province, according to Bacolcol.
General Santos, a port city of more than 700,000 people that is a hub for the tuna export industry and other commerce, was among the hardest hit.
Philippine President Ferdinand Marcos Jr said "the national government is moving and we will not leave Mindanao behind".
The Pacific Tsunami Warning Center said the threat of a tsunami largely passed about five hours after the quake.
At least seven people were killed and about 130 others injured in General Santos, where a few small buildings partially collapsed and several structures, including a key access bridge, sustained dangerous cracks, Rod Sosmena, regional director of the Office of Civil Defence, told The AP.
Nine other people were killed mostly due to falling debris, a damaged mosque and a landslide in the southern provinces of South Cotabato and Davao Occidental and on Balut Island, Sosmeña and another disaster-response official, Ednar Dayanghirang, said.
Sosmena said authorities were checking reports of some students being trapped in a two-storey school that collapsed in General Santos.
He could not immediately provide details but the national police said at least seven people were missing in General Santos.
Public schools had reopened nationwide on Monday after summer holidays.
Dayanghirang said more than 100 students attending morning flag-raising ceremonies in his southern region sustained bruises and some fainted in panic.
The international airport in General Santos was temporarily shut, and 17 domestic flights were cancelled, civil aviation officials said.
DZRH radio in Manila reported that a small commercial building where its provincial station was located partly collapsed and staffers dashed to the ground floor without injuries.
It was not clear if other people were trapped in the rubble of the four-storey office building.
Waves of one metre were generally monitored in the provinces of Sultan Kudarat and Sarangani.
A 1.4m wave was monitored at one time in the coastal area of Kiamba town in Sarangani, Bacolcol said.
The quake was also felt in Malaysia's Sabah state on Borneo island.
An 83cm tsunami was measured by a gauge off Indonesia's Sulawesi island, and the PTWC said 30cm waves were measured in Palau.
Waves up to 20cm were detected on the remote Japanese island of Chichijima and the central Japanese town of Kushimoto, the Japan Meteorological Agency said.
The US Geological Survey reported the depth of the original quake at 55km.
Aftershocks as strong as 6.5 magnitude were recorded.
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.
