Mexico City - Tens of thousands of villagers from the area around the Popocatepetl volcano were set to spend Christmas in shelters, as the volcano spewed clouds of ash-filled smoke and water vapour on Sunday.
Ramon Pena Melche, director of the agency that monitors Popocatepetl, told Notimex news service that a moderate explosion in the cone at 3.55pm (2155 GMT) caused a cloud of smoke to extend as as high as five kilometres from the crater base.
The volcano began its latest spate of activity on December 13, but had shown little sign of activity since Wednesday.
More than 40 000 people were evacuated early this week from communities around the volcano, although in recent days a number are reported to have returned home, sometimes ignoring official warnings.
In shelters housing evacuees on Sunday, villagers were served a Christmas Eve meal of chicken and soup, with fruit punch and gifts for the children.
Popocatepetl's crater is approximately 900 metres wide.
It is one of the most active volcanos in the Americas, situated between the states of Puebla and Morelos, 56km south of Mexico City.
Moderate eruptions have been frequent over recent years and the volcano is often topped by a plume of steam.
The closest village is barely 8km from the crater, and Mexico's national disaster prevention centre has prohibited any villager from returning to the area within a 13km radius of Popocatepetl.
The centre's director, Roberto Quass, said on Sunday that aerial photographs indicated that accumulated lava held in the dome was ready to be expelled.
An expulsion of this lava "has to happen".
"The possible timing clearly can only be estimated. There is no strict formula," he said.
"We don't anticipate it will be a huge event. Rather, we thing there may be a number of incidents over a longish period of time" in the coming weeks or possibly months, he added.
Volcano experts fear that the eruptions and heating of the glacier-capped cone could trigger mudslides, causing more widespread damage than the eruptions themselves. - Sapa-AFP