Mayon Volcano in Albay province, 360 kilometres south-east of Manila, has been erupting since December 14, forcing 47,563 residents to flee their homes at the foot of the mountain.
The victims were a 3-year-old boy who died from parasite infection and three elderly residents who suffered heart attacks, said Luis Mendoza of the provincial health office.
The deaths occurred in different evacuation centres in two towns and one city, he said.
Mendoza said the deaths were caused by "existing conditions" that were not a direct result of Mayon's eruption or the mass evacuation.
But he admitted that the ailments could have been exacerbated by the harsh conditions in 29 evacuation centres, where respiratory and skin diseases have become rampant.
"We are doing health surveillance everyday," he said, adding that at least 10 medical teams from the Department of Health and the military were helping local doctors check on evacuees.
The Philippine Institute of Volcanology and Seismology said the volcano continued to eject lava, rock fragments and plumes of ash reaching as high as 2 kilometres into the air.
The institute warned that if recent rains over Albay become more heavy or prolonged, they could trigger mudslides.
"Active river channels and those perennially identified as prone to mudslides should also be avoided," it said.
The 2,472-metre volcano has erupted about 50 times since 1616. It last erupted in July 2006, forcing more than 30,000 people to flee their homes.
While no deaths were reported during an eruption in 2006, a typhoon triggered deadly mudslides down the slopes two months later, killing nearly 1,000 people.
Mayon's most deadly eruption was in 1814, when more than 1,200 people were killed and a town was buried in volcanic mud. An eruption in 1993 killed 79 people. dpa gl tl se
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