Lava is spilling from a Philippine volcano that has been sending up columns of ash over farmland and towns, coating them in grey during a nearly two-week eruption.

More than 74,000 people are staying in dozens of emergency shelters after fleeing the danger zone around Mount Mayon. Officials are worried the eruption may last months, disrupting the lives and livelihoods of people in its shadow.

Lava flows from the crater of Mount Mayon volcano Photograph: Romeo Ranoco/Reuters

The Philippine Institute of Volcanology and Seismology said on Friday that lava eruptions had been intense but sporadic over the previous 24 hours. It measured ash plumes rising up to 5km (three miles) and detected 15 volcanic earthquakes as well as emissions of sulphur dioxide.

GPS and other measurements from instruments installed around the volcano also continued to indicate a swelling of the mountain surface, consistent with magma rising and creating pressure. The lava coming out may be relieving that pressure, scientists said.

Lava flows down the slope of Mount Mayon as seen from Legazpi in Albay province Photograph: Acayan/Sipa USA/REX/Shutterstock

“It just means that the pressure is being relieved for the moment and then it builds up again,” said Paul Alanis, research specialist at the volcano institute.

The alert level for Mayon remained at four on a scale of five, indicating a violent eruption may be imminent.

No injuries had been reported but law enforcement struggled to keep people out of the danger zone within 8km of the crater.

Mayon volcano spews molten lava during its sporadic eruption Photograph: Bullit Marquez/AP

Officials said temporary learning centres were being set up in the schools that were housing evacuees, while farm animals would be moved so education and income would not be lost.

Farmers have had to leave their rice, vegetable and poultry farms within the danger zone. The initial damage to agriculture alone during the past two weeks exceeded $2m, said Abay provincial agricultural officer Cheryll Ribeta.

Residents look on as Mount Mayon erupts Photograph: Acayan/Sipa USA/REX/Shutterstock

Mayon, in north-eastern Albay province, has erupted about 50 times in the last 500 years. In 2013 an ash eruption killed five climbers who had ventured near the summit despite warnings.

The Philippines has about 22 active volcanoes. The explosion of Mount Pinatubo in 1991 was one of the biggest volcanic eruptions of the 20th century and killed hundreds.