Lava threatens to run downhill, toward Banos, with 15,000 residents, he said.

"This has happened before and could affect Banos," he said.

"The town will have to make its decisions" on whether to evacuate," he said.

So far, a four-kilometer (2.5-mile)-high column of ash has done the most damage, affecting some 100,000 people who live on area farms.

"Farmers in the region are losing everything," said Patricio Donoso, president of the chamber of farmers.

"Some 5,000 hectares (12,000 acres) are damaged," he told Teleamazonas television news.

"We need to distribute hay so that the cattle will not die, and help those who are losing everything."

Some 5,500 women, children and elderly people have been evacuated from the area, Civil Defense authorities told AFP.

The volcano is 5,029 meters (16,500 feet) high and 135 kilometers (85 miles) south of Quito. Since Friday it has released lava and a column of ash.

The volcano erupted in a similar fashion in 1918, with six to eight periods of explosive activity sending lava down its sides, Samaniego said.

"We have not seen this phenomenon since then," he told Ecuavisa television.

President Alfredo Palacio visited the area with five ministers and promised 4.9 million dollars for the emergency.

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A world of storm and tempest