On Monday, the Philippine Institute of Volcanology and Seismology (Phivolcs) raised its alert on the Mayon volcano to level 4, signifying a hazardous eruption is imminent.
Dr Renato Solidum, the Phivolcs agency chief, expanded the to five miles (8km) from the crater.
Mayon volcano update LIVE: Alert level 4 issued – IMMINENT eruption in Philippines warning
More than 27,000 villagers have fled since Mayon started acting up more than a week ago.
And even more are expected to pack up and move now the danger zone has been expanded.
Dr Solidum said: “We strongly advise all people, both residents and tourists, to avoid the danger zone, and airlines to avoid flying near the volcano summit.”
He added Phivolcs recorded increased seismic activity and “lava fountaining and a summit explosion” from Sunday night, indicating more explosions ahead – including a hazardous eruption.
When will Mount Mayon volcano erupt?
A level four alert warning suggests a volcanic eruption is “imminent” and will occur within days.
Although experts cannot predict exactly the eruption will take place and cannot give certain dates, it is likely the volcano will blow this week.
The alert level was upgraded from level three today, which means a “hazardous eruption is possible within weeks or even days.”
At the time, the Phivolcs website stated: “Alert Level 3 remains in effect over Mayon Volcano, which means that it is currently in a relatively high level of unrest as magma is at the crater and hazardous eruption is possible within weeks or even days.”
Professor Rothery said: “Phivolcs is concerned about a lava dome that is growing inside the crater, which may become too steep so that it might collapse, sending pyroclastic flows mainly down the southern side of the volcano.
“If that happens, there will be an ash column too, which will rain ash downwards in the downwind direction – this is less hazardous to people on the ground than a pyroclastic flow.”
A level 4 alert means Mt Mayon is active, with persistent tremors, low frequency type earthquake.
The sulphur dioxide emission level may show sustained increases, as an intense crater glow is recorded at the mountain.
A loud explosion was heard today, Monday, in the wake of increased activity – which experts say makes a hazardous eruption likelier, prompting authorities to close all schools and urge residents to stay indoors.
The country’s most active volcano has been spewing ash, lava, and pyroclastic material since January 13, displacing close to 40,000 residents.
A level 5 alert signifies a hazardous eruption is underway.