The Philippines’ most active volcano was spewing lava down its slopes on Monday, prompting officials to warn tens of thousands of villagers to be prepared to flee from their homes if the gentle eruption turns into a violent and life-threatening explosion, officials said Monday.

More than 13,000 people have left the mostly poor farming communities within a 3.7-mile radius of Mayon Volcano’s crater in mandatory evacuations since volcanic activity increased last week. But an unspecified number of residents remain within the permanent danger zone below Mayon, an area long declared off-limits to people but where generations have lived and farmed because they have nowhere else to go.

With the volcano beginning to expel lava Sunday night, the high-risk zone around Mayon may be expanded should the eruption turn violent, said Teresito Bacolcol, director of the Philippine Institute of Volcanology and Seismology. Bacolcol said if that happens, people in any expanded danger zone should be prepared to evacuate to emergency shelters.

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"What we are seeing now is an effusive eruption," Bacolcol told The Associated Press. "We are looking at this on a day-to-day basis."

From a distance, Associated Press journalists watched lava flow down the volcano’s southeastern gullies for hours Sunday night. People hurriedly stepped out of restaurants and bars in a seaside promenade of Legazpi, the capital of northeastern Albay province about 8.5 miles from Mayon, many of them snapping pictures of the volcano that’s a popular tourist draw known for its picturesque conical shape.

Mayon's renewed restiveness has also struck fear and brought new suffering.

Marilyn Miranda said she, her daughter and 75-year-old mother, who recently suffered a stroke, fled their home in a village within the danger zone in Guinobatan town on Thursday and sought shelter at a sweltering high school turned into an evacuation center. Her nephew returns to their home each day, as do other men in their impoverished rural neighborhood to guard their houses and farm animals, she said.

From the overcrowded evacuation center, they were terrified to see the bright red-orange lava streaks gushing down Mayon’s slope on Sunday night. "We had this feeling that our end is near," Miranda told the AP, breaking into tears.

Mayon's new eruption was one of back-to-back tragedies that struck Amelia Morales and her family in recent days. Her husband died of an aneurism and other illnesses on Friday and she had to hold his funeral wake in a crowded emergency shelter in Guinobatan because she and her neighbors had been ordered to stay away from their community near Mayon.

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"I need help to bury my husband because we don’t have any money left," Morales, 63, said as she sat near her husband’s white wooden coffin under a flimsy open tent in a corner of the evacuation center. "I cannot do anything but cry."

With its peak often shrouded by the wisps of passing clouds, the 8,077-foot volcano appeared calm on Monday. Bacolcol said red-hot lava was continuing to flow down its slopes but could not easily be seen by people under the bright sun.

The volcano had been raised to alert level three on a five-step warning system Thursday, meaning the volcano was in a state of high unrest and a hazardous eruption is possible in weeks or days.

With lava flowing down from the volcano gently, Bacolcol said the alert level would stay at three but it could be moved up higher if the eruption suddenly turns perilous.

The highest alert, level five, would mean a violent and life-threatening eruption is underway with ash plumes shooting into the sky and superheated pyroclastic streams endangering more communities at Mayon’s lush foothills.

Mayon is one of 24 active volcanoes in the Philippines. It last erupted violently in 2018, displacing tens of thousands of villagers. In 1814, Mayon’s eruption buried entire villages and reportedly left more than 1,000 people dead.

The archipelago is lashed by about 20 typhoons and tropical storms a year and is located on the so-called Pacific "Ring of Fire," the rim of seismic faults where most of the world’s earthquakes and volcanic eruptions occur.

In 1991, Mount Pinatubo north of Manila blew its top in one of the biggest volcanic eruptions of the 20th century, killing hundreds.

A group of young people in Montana who are suing the state government for allegedly failing to protect them from climate change is set to begin a two-week trial on Monday.

Montana has a constitutional obligation to protect residents from the impacts of climate change. The 16 plaintiffs, whose ages range between 5 and 22, will try to persuade state District Judge Kathy Seeley that the state has violated this requirement and has endangered their health and livelihoods.

The state’s Constitution says the government must "maintain and improve a clean and healthful environment" and experts say the case could set a legal precedent in several other states with similar environmental protections written into their constitutions, including Pennsylvania, Massachusetts and New York.

Environmentalists are clinging to the case as a potential turning point for legal challenges as similar suits in nearly every state have been dismissed, according to The Associated Press.

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The plaintiffs in the case argue that Montana officials fail to curb planet-warming emissions while the state pursues oil, gas and coal development, court documents show.

The plaintiffs also allege the state is not doing enough to combat smoke from worsening wildfires, which they say is polluting the air, or to alleviate drought which is causing rivers to dry up that would otherwise sustain agriculture, fish, wildlife and recreation.

The state claims that fossil fuel investments provide jobs, tax revenue and help meet the energy needs of residents.

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The state is also expected to argue extreme climate conditions have existed for centuries and that Montana makes "minuscule" contributions towards global greenhouse gas emissions, The AP reported.

The case comes as the National Oceanic Atmospheric Administration said earlier this month the carbon dioxide levels in the air this spring reached the highest levels in over 4 million years.

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The International Energy Agency, which provides authoritative analysis and policy recommendations, said greenhouse gas emissions also reached a record last year.

Judge Kathy Seeley has said she could rule in favor of the environmentalists but cannot tell the legislature how to remedy the violation.

The Associated Press contributed to this report.