Some 8,000 people living near the Galeras volcano on the southern border with Ecuador were evacuated as a precaution late on Thursday after the mountain erupted causing no reported injuries, officials said.
"The protocol dictates that local mayors have to evacuate high-risk area inhabitants. These people must head to shelters or safety zones," said Narino department government secretary Guillermo Garcia.
Authorities said high-risk areas include Pasto city, 920 kilometers (570 miles) south of Bogota, and the towns of Sandona, Narino, Yacuanquer, Consaca and Genoy.
In all, some 8,000 people have been asked to evacuate their homes, they added.
"The eruption was a little strong, but according to the Pasto Vulcanology Observatory it's not serious," Garcia said.
"However, we have to follow the entire protocol, which the inhabitants of the high-risk area know very well," he added.
He said the 400,000 residents of Pasto have been "specially advised to stock up with water, gas masks and flashlights."
The 4,276-meter (14,028-foot) active volcano, which overlooks Pasto, began erupting at 8:06 pm (0106 GMT Friday).
It last erupted in 1992, 1993, 2004 and 2006. In 1993, Galeras killed nine people.