Tungurahua, about 130km south of Quito, has been increasingly active since May, when it began blow out big clouds of hot gas and prompted officials to renew a limited state of emergency in nearby towns.
Civil defence authorities and police said they have evacuated 3,600 people from seven villages around the volcano, the name of which means "throat of fire".
Local scientists say the current activity is the volcano’s strongest since it erupted in 1999.
In the past two days molten rock has set fire to trees and grass, and lava flows have blocked roads and destroyed bridges forcing farmers to flee their land in the volcano’s folds.
The chief scientist of the local geophysics institute, Patircio Ramon, said the volcano "is entering a new and different stage with more violent releases of magma and energy".
"We need to be prepared for the worst ... even though the volcano's activity decreased on Saturday," he said.
During a four-hour visit to local villages, Alfredo Palacio, the Ecuadorean president, said the country needs to prepare "for the worst-case scenario" and promised $5.7 million in relief funds for the region.
Tungurahua has been
increasingly active since May
High alert in the Philippines
Residents were also on the move in the Philippines as thousands of people in six towns in Albay province packed their belongings and prepared to flee their farms and homes because of increased volcanic activities in Mount Mayon in the last 24 hours that prompted authorities to raise the alert level on Friday.
A 6km danger zone was imposed around Mayon, but was widened to 7km on the southeast slope, facing Legazpi City.
About 60,000 people in the province in the central Philippines would be evacuated in the event of a large eruption,a disaster official said on Saturday.
Mayon has erupted about 50
times in the last 400 years
The Philippine Institute of Volcanology and Seismology has also been watching Bulusan volcano in nearby Sorsogon province after it spewed ash and vented steam in March. Last month, volcanologists raised the alert level there to 2.
The Philippines lies on the "Ring of Fire", a belt of volcanoes that circles the Pacific Ocean, which is also prone to earthquakes.
Mayon is the most active volcano in the country, having erupted about 50 times in 400 years. The most destructive eruption came in February 1841 when lava flows buried a town and killed 1,200 people.