A landslide piled into one of Colombia's busiest highways Wednesday, killing at least six people and leaving an "undetermined" number missing and feared buried, authorities said.

The huge mass of brown earth swallowed up a section of road located several kilometers (miles) outside second city Medellin, on a highway that leads to the capital Bogota.

"We have so far located six people, all of them deceased," said disaster management chief for the northwestern department of Antioquia, Gilberto Mazo.

"There is also an undetermined number of people missing," Mazo said, adding that four people were injured and taken to a local hospital.

Mazo put the volume of earth that flooded onto the highway at 50,000 cubic meters (1.8 million cubic feet). He said it was unclear how long authorities need to clean and reopen the highway.

More than 100 rescue workers were combing through the area, which was still on high alert for further landslides.

Authorities blamed the disaster on days of heavy rain in the mountainous area.