An official at the Disaster Prevention Centre's monitoring station said Popocatepetl spat blazing rocks out of its crater at 04.20 GMT on Friday.

Rocks were blasted 4km high

The rocks fell up to five kilometres (three miles) away and national television reports said a light rain of ash was falling on nearby villages.

Rumblings in the 5,452-metre volcano, which lies 65 km south east of Mexico City, have been intensifying for a number of days.

On Wednesday, the mountain, known as Popo, spewed a hail of red-hot rocks and ash more than 4km high.

The following day it sent a huge column of yellowish fumes high into the air. Seven minor eruptions followed before the large blast.

New lava cap

Disaster prevention officials said a new lava cap could be forming in the crater of Popocatepetl, whose name means "smoking mountain" in the Nahuatl Indian language.

Soldiers prevent residents approaching

The Civil Protection service advised residents to keep at least 7km from the crater, avoid going into gorges where lava could flow and keep personal documents close at hand.

A major eruption would force the evacuation of at least 70,000 people who live within a 25km radius.

But officials say it would pose no serious danger to Mexico City and its 18 million inhabitants.

Meanwhile, slow-moving lava continued to flow down the side of another volcano, known as the Volcano of Fire, on the border between the western states of Colima and Jalisco.

About 180 residents have been evacuated from a nearby village and remain in temporary shelters.