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.
The quake also triggered a landslide in Sarangani province in the southern Philippines that killed 13 villagers.
Rene Punzalan, a disaster-mitigation official for the province, told the DZBB radio network that the landslide hit houses in the mountainous town of Glan.
Four other villagers died in Sarangani for still-unclear unclear reasons, he said.
"Our pick-up truck suddenly jerked and I thought we had a flat tire," said Rod Sosmena, regional director of the Office of Civil Defence, told The Associated Press from the hard-hit port city of General Santos, where he was travelling when the quake struck at 7.37am.
"The shaking was very strong and people dashed out of houses into the streets," Sosmena said.
General Santos is a port city of more than 700,000 people that is a regional hub for the tuna export industry and other commerce.
The quake, the strongest to strike the country so far in 2026, was centred at sea off Mindanao, the second most populous island in the Philippine archipelago.
According to the Philippine Institute of Volcanology and Seismology, the quake occurred at a depth of 33km.
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 Pacific Tsunami Warning Center said the threat of a tsunami largely passed about five hours after the quake.
Philippine officials also lifted a tsunami warning by mid-afternoon.
Six shanties on stilts were damaged in a coastal village in Zamboanga del Sur due to the quake and taller waves, officials said.
The Office of Civil Defence said earlier that at least 19 people were killed, mostly in collapsed buildings and landslides, while thousands of villagers were displaced,
Among the dead were seven people in General Santos, where a few small buildings collapsed or were severely damaged, Sosmena said.
The other deaths were caused by falling debris, a damaged mosque and a landslide in the southern provinces of Sarangani, South Cotabato and Davao Occidental and on Balut Island, Sosmena and another reginal 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.
Public schools had reopened nationwide on Monday after the summer holidays.
Dayanghirang said more than 100 students attending morning flag-raising ceremonies in his southern region suffered bruises and some fainted in panic.
Waves of 1m were monitored in the provinces of Sultan Kudarat and Sarangani, and a 1.4m wave was monitored at one time in the coastal area of Kiamba town in Sarangani.
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 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.
