Bogota, Jul 2 (IANS/EFE): A volcano in Colombia has erupted, sending a plume of ash and vapour 10 km into the sky, officials said.

The volcano erupted at 5:40 p.m. Saturday, authorities said.

Subsequently, given the decrease in emissions of ash and gases, authorities downgraded the prevailing volcano alert from red to orange, the Colombian Geological Service said Sunday.

"There has been a considerable decline in the magnitude of the seismic signal associated with the eruption, with respect to the start of it, and so the eruptive event is considered to have ceased," the geological service said.

The volcano's activity continues to change in important ways, however, and authorities are not ruling out the possibility of new eruptions.

Scientists had reduced the alert level from orange to yellow May 29 as a result of seismic changes, the volcano's instability and the emission of ash from the mountain's peak.

About 20 towns in Caldas and Tolima were substantially affected in November 1985 when the Arenas crater erupted, thawing ice and snow on the mountain and causing flooding that killed some 23,000 of the 25,000 residents of the town of Armero.