A 6.0-magnitude quake hit off the Philippines' main island of Luzon on Wednesday, seismologists said, but there were no immediate reports of casualties and no tsunami warning was issued.
The quake's epicentre was off the western coast of the northern province of Zambales, about 230 kilometres (142 miles) northwest of Manila, the US Geological Survey said.
"This won't cause much damage because this is far from land," said Renato Solidum, chief of the Philippine government's volcanology institute.
The earthquake was barely noticed in the capital Manila and in other major cities, said institute researchers.
However, aftershocks were expected, the agency added.