A small volcano near the Philippine capital belched a dark plume of steam and ash into the sky in a brief explosion Thursday, prompting officials to start evacuating thousands of villagers from high-risk areas.

Government experts said magmatic materials came into contact with water in the main crater of Taal Volcano in Batangas province, setting off the steam-driven blast with no accompanying volcanic earthquake. They said it’s unclear if the volcanic unrest could lead to a full-blown eruption.

“It’s just one explosive event; it’s too early to tell,” Renato Solidum of the Philippine Institute of Volcanology and Seismology said at a news conference, adding similar steam-driven explosions may occur.

The agency raised the alarm at 1,020-foot Taal, one of the world’s smallest volcanoes, to the third of a five-step warning system, meaning “magma is near or at the surface, and activity could lead to hazardous eruption in weeks.”

Alert level 5 means a life-threatening eruption that could endanger communities is underway.

Mark Timbal, a spokesman for the government’s disaster-response agency, said officials started to preemptively evacuate residents from five high-risk villages. Up to 14,000 residents may have to be moved temporarily away from the restive volcano, he said.

Officials reminded people to stay away from a small island in a scenic lake where Taal is located and is considered a permanent danger zone along with a number of nearby lakeside villages.