BOGOTA, Feb 19 (Reuters) - Colombian authorities ordered villages evacuated on Monday after the Nevado volcano in the southwestern province of Huila belched ash and increased seismic activity threatened to trigger larger eruptions.

"We expect the volcano to continue erupting," said Alberto Nunez, head of Colombia's Geology Institute.

The evacuation order affects towns located near rivers in Huila and three other provinces that could be hit by avalanches caused a major eruption.

Nunez said Monday's eruption caused a landslide on the banks of one river and more were feared. No victims were immediately reported.

The biggest natural disaster in Colombian history occurred in 1985 when the central Nevado del Ruiz volcano erupted, killing more than 25,000 people.

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