"The eruption is going on right now and continues to generate pyroclastic flows" of red-hot gas, ash and rocks down the volcano's western flank, Geophysical Institute director Hugo Yepez told reporters.

The 5,029-meter (16,500-foot) mountain, 135 kilometers (84 miles) south of the capital Quito, began erupting with a series of loud explosions in the pre-dawn hours, waking more than 20,000 people living in 10 towns and villages in its surroundings.

The eruption so far has caused no injuries or damage, outside of tonnes of ash deposited on buildings and roads in Quero forcing its inhabitants to wear masks.

But some 400 families living closest to the volcano have been evacuated as a precaution.

"Most of the population has left, but we've got 12 families in Bilbao who refuse to leave and we're talking to them. If necessary, we'll use force" to evacuate them, said Tungurahua Province Governor Fernando Gonzalez.

Ecuadoran President Rafael Correa has put the region under a state of emergency to release federal funds and assistance programs.

Shelters and emergency centers in Tungurahua and nearby Chimborazo and Bolivar provinces have been put on standby in case the eruption takes a turn for the worse, said Internal and External Security Minister Gustavo Larrea.

"The volcano has now gone into a period of zero-activity, and that's not good news. It could mean a bigger explosion is in store in the next minutes or hours. But we're ready," Larrea told reporters.

The Tungurahua volcano has been active since last month, with up to 30 explosions, earthquakes or rumblings per hour that forced 1,000 people to relocate to safer areas.

Wednesday's eruption, however, was similar to an August 2006 eruption that killed six people, buried several communities under ash and made 6,500 people homeless, the Geophysical Institute reported.

All rights reserved. � 2005 Agence France-Presse. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by Agence France-Presse. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of Agence France-Presse.