Motorists were forced to turn on their windscreen wipers and headlights as huge quantities of ash and sand rained down following an "intense" explosion from the Philippines' most active volcano.
Following the latest activity by Mount Mayon on Sunday, authorities have raised the alert level from three to the second highest level of four, meaning that a "hazardous eruption is imminent".
The Philippine Institute of Volcanology and Seismology has warned that the volcano was experiencing "intense unrest".
The sun above the southeastern city of Legazpi was blotted out, as local television showed a giant mushroom-shaped clout of ash rising several miles above the volcano after the explosion at midday.
The volcano has been spewing ash, lava, and other material for over a week, forcing some 40,000 residents in the central province of Albay to flee.
Albay Governor Al Francis Bichara said all schools would be closed on Tuesday and the danger zone has been expanded from 6km (3.7m) to 8km (5m) around the crater.
Mayon, located on Luzon Island, is considered the most volatile of the Philippines' 22 active volcanoes and rises 2,460m (8,070ft) above Legazpi, which is home to about 200,000 people.
The Institute of Volcanology director Renato Solidum said: "We expect the explosions to continue. There is a possibility of a dangerous eruption, the start of which we are already witnessing."
He has advised that officials continue to evacuate areas around the crater, with the institute having previously warned of "the danger of rockfalls, landslides and sudden explosions or dome collapses that may generate hazardous volcanic flows".
Despite the warnings, some locals are still yet to leave.
Housewife Girlie Panesa, 39, had to ask for water from bystanders as she made her way home to her daughter, with ash having covered the visor of her motorcycle helmet.
"I had to stop because my helmet had filled up with ash," she said, as she parked her bike by the roadside in Ligao town, which is not far from the volcano.
Residents have been urged to protect against inhaling the ash by wearing masks or covering their noses and mouths with damp cloths, and even those outside the danger zone have been warned to take precautions against potential roof collapses due to the weight of ash and rainfall.
Mayon last erupted in 2014, with lava flows forcing thousands of people to evacuate, and was at its most deadly in February 1841, when 1,200 people were killed and lava buried a town.
But the most powerful explosion to hit the Philippines in recent times was from Mount Pinatubo, around 100km (62m) northwest of Manila, which killed more than 800 people when it erupted in 1991.
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