A large fire ravaged a 19th century palace Tuesday that houses the upper chamber of Egypt's parliament, with flames bursting through windows as helicopters scooped water from the nearby Nile River to try to douse the flames.

Firefighters appeared to be struggling in efforts to put out the blaze: Dozens of fire trucks rushed to the scene but only two were seen spraying water hours after the fire erupted.

There was no official word on the cause. Evacuated employees said authorities told them they had ruled out terrorism, and that an electrical short circuit had likely sparked the fire.

Six workers and firefighters were hospitalized for smoke inhalation, said Ahmad Salah, the fire operations supervisor.

Flames soared upward from the top floor of the three-story building, and much of the interior appeared gutted. While firefighters focused on one corner of the building, the blaze burned heavier on a second corner, spreading to the second floor.

Two helicopters ferried buckets of water from the Nile and poured them onto the blaze.

Thick black smoke billowed over downtown Cairo, and rush hour traffic gridlocked from the fire trucks.

Riot police created a cordon outside the parliament complex, located on a busy downtown thoroughfare. Tourists and locals stopped to snap photographs with cell phone cameras.

The extent of damage was not immediately known.

Egypt requires some fire-safety measures in buildings, including fire extinguishers, but in general the rules are not strictly enforced.

The country's deadliest blaze was in February 2002, when flames swept through a crowded passenger train south of Cairo, killing 370 people.