MANILA - A series of tremors that rocked Batangas province on Saturday were part of an "earthquake swarm," caused by the movement of a local fault line, the Philippine Institute of Volcanology and Seismology (PHIVOLCS) said Sunday.

Phivolcs director Renato Solidum said the earthquake swarm has been going on since Tuesday night and seismologists have recorded over 1,000 quakes, including Saturday's 3 "moderately sized" tremors.

"Iyung naitala pong paglindol sa Batangas, nagsimula ng April 4 ng gabi. Mayroon pong series ng mga lindol, sunod-sunod at wala masyadong distinct na malaki -- magkakalapit lang po ang magnitude. Ang tinawatag po namin diyan ay earthquake swarm. Ibig sabihin ay paunti-unting gumagalaw ang fault," Solidum told radio DZMM.

(The earthquakes in Batangas started on the night of April 4. There was a series of quakes, which were successive and had almost similar magnitudes. We call this earthquake swarm. It means that a local fault is slowly moving.)

Earthquakes jolted Mabini town in Batangas Saturday afternoon a minute apart: first a magnitude 5.7 at 3:08 p.m., followed by a magnitude 5.9.

A third quake hit Taysan town in Batangas 20 minutes later at magnitude 5.0.

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The quake's origin is close to the island town of Tingloy, where a 5.5-magnitude quake hit just before 9 p.m. Tuesday. It generated multiple aftershocks.

The still unnamed fault that caused the tremors had first shown movement last year, but had only triggered moderate-sized earthquakes this month, Solidum said.

He also warned the public that more earthquakes may rattle Batangas.

"Iyung mga swarm po, ang tagal niyan ay araw o linggo. Talagang magkakaroon pa po ng mga lindol, marami pa po, maliit," he said.

(An earthquake swarm typically lasts for days or weeks. There would be more minor earthquakes.)

The Batangas quakes however are too far from the West Valley fault to cause tremors in Metro Manila, Solidum said.