The seismological agencies of the Philippines and Indonesia have issued tsunami warnings, while the Pacific Tsunami Warning Center issued an alert also for Palau, Taiwan and Papua New Guinea.
"We advise people to evacuate to higher grounds or go further inland," said Teresito Bacolcol, director of the Philippine Institute of Volcanology and Seismology (Phivolcs).
Phivolcs warned that tsunami waves above one meter (yard) could continue for several hours, while aftershocks could also be felt in the region.
Philippine President Ferdinand Marcos Jr. said authorities were moving fast to coordinate disaster response.
"The national government is moving and we will not leave Mindanao behind," Marcos said in a statement.
Indonesia lifted its tsunami warning later on Monday.
The Philippines lies on the edge of the Pacific's so-called 'Ring of Fire' — an arc of seismic faults that makes the country unusually prone to volcanos, earthquakes and tsunamis.
At least 3 killed, several injured in earthquake
Police on Mindanao reported that at least three people were killed and several others were injured by the earthquake as reports of damage began to emerge.
"Many buildings were affected, but I cannot enumerate them now because we are busy with ongoing rescues," Master Sergeant Robert Dagon of the General Santos City police told the AFP news agency.
"A number of buildings collapsed. Some houses also collapsed."
The quake struck 24.7 kilometers (15.3 miles) west-southwest of the Philippine town of Burias at a depth of 35 kilometers (22 miles), according to the US Geological Survey.
