A magnitude-5.9 earthquake has hit off the northern coast of the Philippines, the United States Geological Survey said.

The strong quake, initially reported as a magnitude 6.1, struck today at 3:58 am local time.

Its epicentre was in Luzon, 42 kilometres north-east of Laoag, at a depth of 42.5 kilometres below the seabed.

A magnitude-5.9 quake is capable of causing considerable damage, but there are no reports of damage so far.

-Reuters