A raging fire damaged nine buildings Wednesday afternoon in this city across the Hudson River from lower Manhattan, forcing dozens of people from their homes. Nine firefighters collapsed from heat exhaustion, authorities said. The fire broke out shortly after 5 p.m. in a residential area of the city and was declared under control about two hours later. Authorities were investigating whether the blaze might have been touched off by an electrical explosion, Fire Director Armando Roman said. All residents of the buildings escaped safely. Roberta Harper was in her apartment next to the building that initially caught fire when she smelled smoke and ran outside. “It was like the whole block blew up,” she said. “There was smoke and fire everywhere.” Smoke blanketed the area and could be seen from miles away on a day when the temperature was in the high 90s. Nine vehicles parked on the street also were destroyed.