MANILA - A 5.6 magnitude earthquake struck the waters off Isabela province at 5:19 p.m. Sunday, state seismology bureau Phivolcs said.

Phivolcs said the tremor struck some 18 kilometers northeast of Maconacon town, with a depth of 55 km.

The quake was tectonic in origin.

The following instrumental intensities were reported:

Intensity V
- Penablanca, Cagayan

Intensity IV
- Gonzaga, Cagayan

Intensity III
- Ilagan, Isabela

Intensity II
-Casiguran, Aurora
- Batac, Pasuquin, and Laoag City, Ilocos Norte
- Santiago City, Isabela,
- Tabuk, Kalinga
- Madella, Quirino

Intensity I
- Bangued, Abra
- Baler and Diapaculao, Aurora
- Vigan City and Sinait, Ilocos Sur
- Bayombong, Nueva Vizcaya

Aftershocks are expected from the tremor, but no damage is expected, Phivolcs said.