"It was a really big shake coming from the volcano and that forced civil defense to evacuate the population," said civil defense chief Roberto Rodriguez.

He said there were no reports of injured or dead, but local authorities said ash and rock fragments showered hamlets located on the slopes of the volcano, which erupts powerfully every hundred years or so.

In 2006, streams of fast-moving molten rock enveloped several hamlets tucked in the volcano's folds, killing at least four people and forcing thousands to evacuate and lose their corn and potato crops.

Classes were canceled and roads closed in the area around the mountain on Wednesday. Officials did not evacuate the nearby Banos hot springs, a popular destination for foreign tourists, but volcano experts said they had not ruled out that lava could reach the town.

In 1999, 17,000 people were forced to evacuate the town of Banos after loud explosions and hot gas blew from the volcano.

Volcanologists expect still stronger activity from Tungurahua, which is in the middle of an eruption cycle that began in 1999.

"This is an ongoing eruption and we still don't know the magnitude it could reach," said Hugo Yepes, the head of the country's Geophysics Institute.

Juan Salazar, the mayor of Penipe, a municipality near the volcano, said on Wednesday that Tungurahua sounded like "an old airplane turbine."