The Disaster Risk Management Office said it was moving to evacuate communities that are located within 15 kilometers (nine miles) from the main crater of three that make up the Nevado del Ruiz volcano in the Colombian Andes.
Seismic activity has increased at the volcano, which killed 25,000 people in an eruption in 1985.
That blast was the worst natural disaster in Colombian history and one of the deadliest volcanic eruptions of the 20th century.
There has recently been a “significant increase in seismic activity,” the ministry of mines said in a statement while Colombia’s SGC geological service warned of a “probable eruption within days or weeks.”
The 5,300-meter (17,400-foot) colossus in western Colombia is one of the many volcanoes along the Ring of Fire, a path around the Pacific basin characterized by active volcanoes and frequent earthquakes.
On November 13, 1985, it erupted and emitted so much heat that it melted the snow that caps the mountain.
This triggered a cascading wall of mud that swallowed the town of Armero, killing half its population of 50,000.