Authorities in the Philippines are warning people to stay clear of the volatile Mount Mayon volcano after multiple eruptions overnight spread lava and ash for kilometers.
A thick column of ash streamed five kilometers into the air above the volcano, in Albay province in southeastern Luzon, and spread over neighboring districts, the Philippine Institute of Volcanology and Seismology (PHIVOLCS) said in a statement Tuesday.
Falling ash left Guinobatan, a town of around 80,000 people, in a state of "zero visibility," according to affiliate CNN Philippines.
PHIVOLCS said it had also detected "two explosion-type earthquakes" as well as dozens of rockfalls and "lava fountaining episodes" in and around the crater on Monday.
The alert level for Mayon volcano -- the country's most active volcano -- was raised to four from three last week after it exhibited increasing seismic unrest and summit explosions. The highest level -- five -- means a hazardous eruption is underway.
More than 27,000 people have been evacuated from the area around the volcano in preparation for a dangerous eruption. Lava has been flowing down from the crater since last week.
The public has been advised to stay vigilant and avoid the danger zone, which covers an eight-kilometer (five mile) radius from the volcano summit, according to the agency.
"The evacuation has been ongoing since [the volcano] started showing signs of instability," Mark Dambal, information officer at the Philippines' Office of Civil Defense, told CNN.
"Because of the volcanic activity, the danger zone was extended from six kilometers to eight kilometers [from the volcanic summit]," he added. "People staying in the area are now ordered to be evacuated."
He added that more than 24,000 people have been displaced to evacuation centers across the province, while another 3,100 have moved to stay with relatives and friends.
In a media briefing Monday, the agency's director Renato Solidum warned that this eruption could be similar to that of 2001, which featured pyroclastic flow, according to CNN affiliate CNN Philippines.
A possible pyroclastic flow -- characterized by a rapid movement of hot lava blocks, pumice, ash and gas along volcanic slopes -- could reach up to three kilometers (1.8 miles), Solidum said.
Lava was seen to be flowing more voluminously than before, according to a press release from the agency. It also stated that lava eruptions have resulted in an ash plume of up to 1,300 meters (4,300 feet) above the summit.
Classes at private and public schools have been suspended as a precautionary measure, Albay Gov. Al Francis C. Bichara posted on Facebook. He has also advised residents to wear facemasks and stay indoors.
Situated on the island of Luzon, about 330 kilometers (205 miles) southeast of Manila, Mayon is one of the world's most active volcanoes.
Since 616, it has erupted 47 times, with many of the explosions causing deadly mudflows and ash falls.
In 2014, thousands of residents were ordered to evacuate the same area after an alert was issued, while in 2013, five climbers died when they were hit by falling rocks thrown up by a particularly violent blast.
The volcano's most devastating eruption took place in 1814 when at least 1,200 people were killed.
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