Aftershocks from a deadly earthquake jolted Cairo on Wednesday, toppling more apartment houses but causing no casualties.
Two aftershocks rippled through Cairo and the surrounding area. Ezzeddin Ibrahim, a government earthquake expert, said seismographs registered one at dawn at 3.7 on the Richter scale and another measuring 3.6 six hours later.
President Hosni Mubarak said Monday's earthquake killed more than 450 people and injured more than 4,000 nationwide.
Officials at the government's earthquake operations center refused to say how many buildings fell Wednesday. On a main street in downtown Cairo, police cordoned off an area surrounding two damaged apartment houses.
Before Wednesday's collapses, the government said 536 buildings nationwide had crumbled or were seriously damaged.
Much of the construction in Cairo is so shoddy that the city is known for buildings that fall even without earthquakes.
"Cairo is a time bomb," said Saad Eddin Ibrahim, American University sociologist and urban planning expert. "It just takes catastrophes to bring it out."
In Fayoum, 70 miles southwest of Cairo and close to the epicenter of Monday's quake, many residents spent Monday and Tuesday night sleeping outside for fear of more deadly earthquakes. Thousands ventured inside Wednesday, only to flee again to the streets when the aftershocks struck.