A burning 12-story building collapsed in a Cairo suburb Monday night, trapping at least 18 people inside and injuring 29, police said. All but two of the trapped were firefighters and policemen dispatched to put out the blaze, the officials said on condition of anonymity. Twenty residents and nine police were hospitalized. The officials first said the fire broke out at an Egyptian fast-food restaurant on the ground floor, but later reported it began at an adjacent home appliances store. Most tenants on the upper floors got out before the building collapsed about three hours after the fire started. The building is in Nasr City, an eastern suburb of the Egyptian capital near the airport. The area is home to many high-rise residential buildings and shopping areas. Police sealed off the area and evacuated two buildings that were damaged by the collapse, while firefighters and policemen worked under floodlights to rescue their trapped colleagues. Building collapses are common in Egypt and are often caused by shoddy construction or the unauthorized building of extra stories. The last such incident was May 4, when a seven-story apartment building collapsed in Cairo, killing at least seven people. **PHOTO CAPTION*** Egypt map.