"Now the roof has collapsed. Even the smallest gust of wind makes it grow bigger," he said.
"According to security experts, all options are open, you can never tell the reason behind the fire at this particular moment."
Parliament workers and firefighters were among those hospitalised suffering smoke inhalation and burns, Ahmed Salah, a fire operations supervisor, said.
There was no official word on the cause of the fire, which ravaged the 19th century palace, but state-run television said in a brief statement that the cause was probably a short circuit.
Fire engines that sprayed water from hoses caused parts of the ceiling on the top floor to collapse.
"Parliament is currently on summer recess and very few people would have been in the building," a police official said.
Police forces cordoned off the area around the building in downtown Cairo, which is close to the American University in Cairo and several Western embassies.