Solidum said his team had recorded 1,266 volcanic quakes in the last 24 hours, down from nearly 2,000 the previous day.
But he said while the quakes were fewer, they were more powerful.
The evacuees are being told to prepare for an uncomfortable Christmas, with little sign that it will be safe enough to return home before the holiday season.
Joey Salceda, the governor of Albay province, said patrols were searching the area for about 500 people still thought to be in the evacuation zone.
"We're conducting house-to-house surveying to make sure people will go to the evacuation centres. There is some resistance due to the Christmas season," he told Al Jazeera.
"To keep people in the evacuation centres we're holding concerts and other activities in order to keep people from going home."
Volcanologists have put the alert around Mayon at level four on a five-point scale.
|Authorities say it may be days or weeks before evacuees can return home [AFP]
Level five signifies an eruption is under way.
On Tuesday Mayon sprayed volcanic ash over a wide area, raising new health fears for thousands living around the volcano.
"The main problem of the eruption from a distance is the fine ash which is being generated by the collapse of rock fragments from the lava flow," said Solidum, speaking to Philippines TV.
"It's not very thick, just a few millimetres of ash but that is the most dangerous part because it is very fine ash."
Health officials have said the tiny particles could cause respiratory problems or skin diseases, and could even affect the thousands of people crammed into evacuation centres outside the eight-kilometre danger zone.
In the village of Guinobatan, some 14km from Mayon and well beyond the official danger zone, residents complained of stinging eyes and said they could feel the particles irritating their skin.
Volcanic ash from Mayon has proved extremely deadly in the past.
During the volcano's last eruption in 2006, the volcano oozed lava and vented
steam and ash for two months.
No one was killed by the eruption itself, but three months later, a powerful typhoon dislodged tons of volcanic ash creating an avalanche of mud and boulders that crushed entire villages, leaving more than 1,000 people dead.