There's renewed concern that Colombia's largest hydro-electric dam could be on the verge of bursting. Flooding last weekend forced thousands to evacuate the area. It's the latest set-back for the dam that's still months away from completion. CGTN's Michelle Begue reports.

A cellphone catches the exact moment when dam workers had to run from a flashflood related to work on Colombia's hydroelectric dam-Hidroituango. Clearing a blocked tunnel unleashed a river of muddy water and debris. The deluge swept through a hamlet downstream. Colombian authorities ordered tens of thousands of people downstream from the dam to evacuate their homes.

Now, there is risk the dam could burst. That's according to EPM-the energy company building the dam. More than 100-thousand people in a dozen municipalities live downstream from the dam.

ANA MARIA FAJARDO COOSALUD HEALTH WORKER "This is a tremendous disaster. We are trying to see what machinery we can save."

HECTOR ARROYAVE SURVIVOR OF FLOODING "My hands are tied. I don't know how to make a living moving forward."

According to EPM, a landslide blocked one of the tunnels. Clearing it caused the flood.

JHON MAYA VP BUSINESS MANAGER EPM "We had to move through the engine room was to prevent the water from rising and not have it go over the dam."

Activists are calling for an investigation. They say EPM caused the blockage by failing to clear plant material from dam-related construction work. In a letter published Wednesday night, Colombian President Juan Manuel Santos said: "The Government won't spare any efforts to protect the population." EPM says they have thousands of people working day and night to drain the water and finish the dam. Hidroituango was supposed to be fully operational by the end of the year.

MICHELLE BEGUE BOGOTA "Local environmentalists have long opposed the dam, claiming it will do untold damage to areas along the riverbed. The Colombian government and EPM consider the Hidroituango one of the country's landmark projects. If the dam bursts, it will become a landmark for all the wrong reasons. Michelle Begue, CGTN, Colombia."