Three people were injured and many buildings were damaged in downtown Athens early Wednesday after an explosion rocked a building under renovation and adjacent structures.

A 77-year-old man sustained severe burns to his arms and legs as a result of the explosion and was rushed to a hospital, public broadcaster ERT reported. Two others received medical attention for smoke inhalation.

The predawn blast, which occurred 200 meters (655 feet) from the ancient Temple of Olympian Zeus, also severely damaged three other nearby buildings, causing a traffic jam.

It was not immediately clear what triggered the blast or the fire, officials said. The explosion occurred shortly after 6:50 a.m. (5:50 a.m. GMT) on the first floor of a building that residents said was empty and was being renovated, news channel Skai reported.

The explosion smashed windows and wrecked the facades of buildings and shops along the Syngrou Avenue traffic artery, which links the center of the Greek capital to the southern suburbs, while damaging buildings up to 200 meters away.

Debris and broken glass littered the street, a day after a severe snowstorm swept the city disrupting traffic and stranding thousands of people.

"At the time of the explosion I was exactly across from the building. It was strong, really strong, (you see) the buildings around it," said taxi driver Christos Chalkias. His vehicle's windows were also cracked by the blast.

"The explosion sent us two lanes to the right," he said.

At least 18 firefighters used seven engines to battle a blaze at one building and had nearly brought it under control, the fire brigade said.

"We have a fire, there was a blast before that," said a fire brigade commander at the scene. The crime investigation unit had also arrived at the scene.

Firefighters were using aerial ladders to look for anyone possibly trapped inside the damaged buildings. As dawn broke, they forced their way into damaged stores to free several people trapped inside.