Residents were too afraid to return to their homes as aftershocks rocked a blacked-out northern Philippines Wednesday, hours after a strong earthquake injured at least six people and damaged schools, churches and other buildings.

The 6.4-magnitude quake struck the mountain town of Dolores in Abra province late Tuesday, cutting power to most of the region. Numerous aftershocks rattled Abra through the night and into Wednesday morning, authorities said.

President Ferdinand Marcos Jr ordered a school holiday as authorities assessed damaged buildings and said electricity was being restored.

A building housing a gallery of photos of the presidency of his father, Ferdinand Marcos Sr, in their home city of Batac was among those damaged.

"People are asking for tents, and the reason why is they are afraid of going back to their houses because of the aftershocks, which could collapse their houses with the foundations weakened," Marcos Jr told reporters.

Several patients spent most of the night outside a government hospital in the city after ceilings collapsed on several rooms and damaged equipment, a hospital staff member said.

All patients and staff were safe but the hospital's outpatient department was closed while the building was being inspected.

Rescuer Ron Sequerra said his family had been woken by strong shaking near the epicentre in Abra.

"We hid under a table and my family only went out of the house after the shaking stopped," Sequerra told AFP by telephone. He said six people were injured in Lagayan town.

Workers cleared a Batac road that had been blocked by tumbling boulders, while a number of old churches in Abra and Ilocos Norte also sustained damage, the civil defence office said.

The Lagayan mayor's office in Abra was closed after it sustained cracks and broken windows, as was a newly built high school already damaged by a strong quake earlier this year.

"We had a room in there with old laptops that toppled like dominoes. The walls and the posts were destroyed. It's no longer safe to use," Esterio Apolinar, principal of Lagayan's Pulot National High School, told AFP.

The education department also released photos of upended desks and chairs and books scattered on the floor at other Lagayan schools.

The spire of an old church in the nearby town of La Paz crumbled, scattering blocks of brick on the courtyard, its parish priest Christian Edward Padua told AFP.

Ilocos Norte governor Matthew Manotoc, the president's nephew, told government workers to take the day off while authorities inspected buildings.

Flights were cancelled when the airport in the provincial capital, Laoag City, shut its runway for two days to check for damage, flag-carrier Philippine Airlines said.

A 7.0-magnitude quake in mountainous Abra in July triggered landslides and ground fissures, killing 11 people and injuring several hundred.

Quakes are a daily occurrence in the Philippines, which sits along the Pacific "Ring of Fire", an arc of intense seismic and volcanic activity that stretches from Japan through Southeast Asia and across the Pacific basin.