Up to 325,000 people live in areas that could be threatened by fast-moving mud and rock flows if there is a major eruption of the Cotopaxi volcano in Ecuador, a senior disaster official said.
Maria del Pilar Cornejo briefed reporters as bad weather scrapped a planned flyover of the snow-capped 19,600ft volcano, which is 30 miles south of the capital Quito.
Cotopaxi last rumbled on Saturday, when it shot ash more than two miles high and spilled some lava. Four hundred people were evacuated briefly.
The volcano began showing renewed activity in April. Its last major eruption was in 1877.
President Rafael Correa decreed prior censorship on Saturday on the volcano, worrying press freedom groups. It means that all media are prohibited from publishing information about Cotopaxi that does not come from an official source.