JEDDAH, 29 March — Five expatriate workers were injured, one of them seriously, when the concrete block of a mosque under construction here collapsed. The workers, trapped under the debris, were rescued by Civil Defense officers and rushed to hospital. Col. Muhammad Al-Ghamdi, director of the Civil Defense, said his department has already launched a probe into the accident. A source at Dar Al-Shifa Hospital said the injured were four Pakistanis and an Egyptian.