Millions of people were without power in the southern Philippines on Thursday but authorities have yet to determine a cause of the problem, dpa reported. The blackout hit the entire island of Mindanao, home to more than 21 million people, before dawn, according to Energy Secretary Jericho Petilla. "We are trying to figure out the source of the interruption," he told a Manila radio station. "So far, there are no reports of damaged power plants." The National Grid Corporation of the Philippines said it was "working to restore the power transmission service" to the entire island, and so far had restored supply to five cities