QUITO, Ecuador -- Ecuador's Tungurahua volcano hurled truck-sized pyroclastic boulders more than a mile Friday in a powerful eruption that prompted at least 300 people to flee their homes, authorities said.

Schools were closed for a third straight day as ash showered down on a dozen towns in the sparsely populated area surrounding the 16,480-foot (5,023-meter) volcano.

Thundering explosions could be heard miles from Tungurahua, which is on the Andes cordillera 84 miles southeast of Ecuador's capital, Quito.

A state Geophysics Institute scientist monitoring the volcano from a nearby observation post said by phone that incandescent boulders were landing up to 1.2 miles beneath crater level.

"The smallest blocks are that size of an automobile while the biggest reach the size of a truck, which cause impact craters up to 10 meters (33 feet) wide as they hit the flanks," the scientist, Silvana Hidalgo, told The Associated Press.

She called the eruption level "moderate to high."

Civil defense officials reported an intense shower of ash east of the volcano, including in Banos, a tourist destination three miles away that is popular for its hot springs.

The volcano has been active since 1999. At least four people were killed and thousands evacuated in eruptions in July and August of 2006.