Thick smog surrounded the Taal Volcano in the Philippines on Thursday morning.

Footage shows the toxic haze blanketing the volcano in Batangas province on June 22.

Residents were alarmed after seeing rafts of volcanic rocks floating in Taal Lake on Wednesday, local media reported. Authorities said recent rains may have washed the rocks towards nearby communities.

The Philippine Institute of Volcanology and Seismology (PHIVOLCS) in a bulletin on Thursday, June 22, said it recorded 13 volcanic earthquakes over a 24-hour period. Alert Level 1 - the lowest in a five-step warning system - was still raised over the volcano, PHIVOLCS.

Pregnant women, children, and the elderly, especially those with underlying health conditions, were advised to stay indoors as the fumes were hazardous to their health.

Speaking to local media, PHIVOLCS director Dr. Teresito Bacolcol said: 'We remind residents to limit their outdoor activities as much as possible. They have to wear masks if they go outside.

'As of now, Taal Volcano is still under Alert Level 1. It might lead to a volcanic eruption, but it might not. Under Alert Level 1, there is the possibility of a sudden explosion - steam or phreatic explosion. That's why we are closely monitoring the volcano.'

According to PHIVOLCS, Alert Level 1 indicates 'low level of volcanic unrest'. It warned there may be steam-driven or gas-driven explosions, volcanic earthquakes, minor ashfall, and lethal accumulations or expulsions of volcanic gas.

The Philippines is an archipelago of more than 7,000 islands inside the Pacific 'Ring of Fire' where the majority of Earth's volcano eruptions and earthquakes happen.