A light spewing of ash on Tuesday amid renewed rumblings in the Nevado del Ruiz volcano prompted Colombian authorities to evacuate 500 people from beneath its flanks and briefly suspend flights at four airports.
The volcano's seismic activity was more intense than episodes in April and early May, when it emitted columns of steam, said the government geological agency Ingeominas.
The 5 321-meter volcano spouted ash that fell on population centres including the western city of Manizales, whose airport remained closed on Tuesday evening.
The other affected airports, in Pereira, Armenia and Cartago, resumed normal operations during the afternoon, said Carlos Silva, deputy director of Colombia's civil aviation agency.
The heightened seismic activity prompted Ingeominas to raise the volcano's alert level to orange, meaning an eruption is probable in days or weeks. Such a level has been declared in the past without eruptions occurring.
A 1985 eruption by Nevado del Ruiz buried the town of Armero in a wall of mud, killing about 25 000 people. - Sapa-AP