The Philippine Institute of Volcanology and Seismology revised down to 7 the magnitude and relocated the epicentre of the earthquake that rattled Abra province in the northern Philippines on Wednesday.

The institute first reported the magnitude as 7.3, and the epicenter was Lagangilang town. An updated report changed the epicentre to Tayum town.

The revised bulletin also said the quake, which occurred at 8:43 a.m. local time (0043 GMT), hit at a depth of 17 km, about 3 km northwest of Tayum town, Xinhua news agency reported.

The tremor was also felt in many areas on the main Luzon Island, including Metro Manila, where high-rise buildings swayed and train transport halted operation. It was also felt in many provinces, including Ilocos Sur, Pangasinan, Nueva Vizcaya, Bulacan, Laguna and Cavite.

Panicked employees in several offices, including the presidential palace, ran out of the buildings.

There were no immediate reports of casualties, but a local official told a radio that he received information that the quake triggered stones slides in some areas.

A spokesperson for the regional police said no reports of deaths or injuries so far, saying they received reports of damages to houses and buildings in Abra and Vigan City in Ilocos Sur.

The tremor damaged century-old structures in Vigan City, a tourist destination known for its preserved Spanish colonial and Asian architecture on the west coast of Luzon island.

La Paz town Mayor Joseph Bernos of Abra said the quake damaged many concrete houses, buildings and infrastructure in the province. "I received reports that there were massive damages in our province," he told a radio interview.

He said that some buildings at the University of Abra were also damaged.

A local disaster official of Baguio City, also in the northern Philippines, said Kennon Road was closed while the damage was being assessed.

Renato Solidum, the institute's chief, warned the tectonic quake would trigger aftershocks and could cause damage such as landslides. He urged the people and the local government officials to be vigilant.

"Make sure to inspect the buildings for cracks and watch out for landslides, especially when it rains," he told a news conference, urging villagers to leave areas prone to landslides.

On July 16, 1990, northern Luzon was shaken by a 7.8-magnitude earthquake that caused a 125-km-long ground rupture that stretched from Aurora province to Nueva Vizcaya. The epicentre of the 1990 quake was near Rizal town in Nueva Ecija province. The quake killed around 1,200 people and damaged scores of buildings and houses.

The Philippines has frequent seismic activity due to its location along the Pacific "Ring of Fire.