A small earthquake shook buildings in the Philippine capital of Manila on Wednesday but caused no damage, the government said.

The Philippine Institute of Volcanology and Seismology said the quake had a magnitude of 3.8, and hit in Bulacan province about 50 kilometres (30 miles) to the north of Manila.

"We are not expecting any damage. We also have no reports of any casualties," civil defence chief Benito Ramos told AFP.

Phivolcs seismologist Ishmael Narag said on DZBB radio no aftershocks were expected because it was such a small earthquake.

The Philippines sits on the Pacific Ring of Fire -- a belt around the Pacific Ocean dotted by active volcanoes and unstable ocean trenches.

One fault line runs directly under Manila, a chaotic megacity of about 15 million people, and government seismologists as well as international experts have warned the capital is unprepared for a major quake.