Three laborers doing construction work on the second level of a stretch of highway in the Mexican capital were injured with "scratches" after the huge horizontal beam they were lifting with a crane came crashing down.

The municipal public works department, known as SOS, said in a communique that following the accident, which occurred before dawn on the Periferico Norte highway, they were "working intensely" in coordination with police to get traffic moving again on the heavily traveled road.

Authorities in the capital and in neighboring Mexico state are currently adding a second level several kilometers (miles) long to the Periferico highway, a contract awarded to the Spanish firm OHL.

"When they were maneuvering a beam into place, the crane doing the work had a mechanical failure and the beam fell," SOS said.

Three OHL workers were injured "with scratches" and were pronounced in good condition right on the work site after being seen by paramedics from the Mexican Red Cross.

To end the traffic tie-up, authorities opened the middle lanes, which normally go from south to north, to vehicles going the opposite direction.

The Mexico City government also asked the company that operates part of the Periferico highway to temporarily waive tolls.