At least seven dead after two powerful offshore earthquakes struck southern Philippines

The first 7.4 magnitude tremor killed at least seven people, setting off landslides and prompting evacuations of coastal areas nearby because of a tsunami scare.

The second one had a preliminary 6.8 magnitude and also sparked a local tsunami warning by authorities.

It was caused by movement in the same fault line, the Philippine Trench, at a depth of 37 kilometres (23 miles) off Manay town in Davao Oriental province, Philippine Institute of Seismology and Volcanology chief Teresito Bacolcol said.

"The second one is a separate earthquake, which we call a doublet quake," Mr Bacolcol told The Associated Press (AP).

"Both happened in the same area but have different strengths and epicentres."

Read more: Tsunami threat after 7.6-magnitude earthquake strikes offshore southern Philippines

Read more: Hamas gathering hostages 'now', claims Trump, as thousands of Palestinians make way to north of Gaza

Mr Bacolcol and other authorities expressed fears that the second night-time earthquake could further weaken or collapse structures already undermined by the first one.

President Ferdinand Marcos Jr, facing his latest natural disaster after a recent deadly quake and back-to-back storms, said the potential damage was being assessed and rescue teams and relief operations were being prepared and would be deployed when it was safe to do so.

The first quake was centred at sea about 43 kilometres (27 miles) east of Manay town and was caused by movement in the Philippine Trench at a depth of 23 kilometres (14 miles), government seismologists said.

At least seven people were killed, including two patients who died of heart attacks at a hospital during the first earthquake and a resident who was hit by debris in Mati city in Davao Oriental, Ednar Dayanghirang, regional director of the government's Office of Civil Defence, told The AP.

Three villagers died and several others were rescued with injuries by army troops and civilian volunteers in a landslide set off by the first quake in a remote gold-mining village in Pantukan town in Davao de Oro province near Davao Oriental, Mr Dayanghirang said.

Another resident died because of the first quake in the port city of Davao, disaster mitigation officials said without providing other details.

They added that a few hundred residents were injured in the city.

Office of Civil Defence deputy administrator Bernardo Rafaelito Alejandro IV said that several buildings sustained cracks in their walls, including an international airport in Davao city, but it remained operational without any flights being cancelled.

"I was driving my car when it suddenly swayed and I saw power lines swaying wildly. People darted out of houses and buildings as the ground shook and electricity came off," Jun Saavedra, a disaster mitigation officer of Governor Generoso town in Davao Oriental, told The AP.

"We've had earthquakes in the past, but this was the strongest," Saavedra said, adding that the intense ground swaying caused cracks in several buildings, including a high school, where about 50 students were brought to hospital by ambulance after sustaining bruises, fainting or becoming dizzy because of the first quake.

Governor Generoso is a town about 100 kilometres (60 miles) south of Manay, where school classes at all levels were also suspended.

Children evacuated schools in Davao city, which has about 5.4 million people and is the biggest city near the epicentre, about 250 kilometres (155 miles) west of Davao Oriental province.

The Pacific Tsunami Warning Centre in Honolulu said small waves were detected on the coasts of the Philippines and Indonesia before the threat passed about two hours after the first quake. It said small sea fluctuations may continue.

A tsunami warning that set off evacuations in six coastal provinces near Davao Oriental was later lifted without any major waves being detected, Mr Bacolcol said.

Indonesia's Meteorology, Climatology and Geophysics Agency said small tsunami waves were detected in North Sulawesi province with heights ranging from 3.5 to 17 centimetres (1.3 to 6.7 inches) in Melonguane, Beo, Essang and Ganalo in Talaud Islands districts.

The Philippines is still recovering from a September 30 earthquake with a 6.9 magnitude that left at least 74 people dead and displaced thousands of people in the central province of Cebu, particularly in Bogo city and outlying towns.

The archipelago is also lashed by about 20 typhoons and storms each year, making disaster response a major task of the government and volunteer groups.