"There are six dead and 11 people were rescued alive," a fire department spokesman told AFP in an updated toll. "We do not know exactly how many more people there are under the rubble."
Local press reports said 19 people were injured in the accident.
Television pictures showed extensive damage as rescue workers frantically sifted through rubble in search of survivors.
The cause of the accident was not yet known.
More than 20 fire department vehicles and two helicopters were on the scene.