Rescuers were searching for four people Sunday after a boat carrying more than a dozen scuba divers sank at a World Heritage-listed marine sanctuary in the Philippines, authorities said. The Philippine Coast Guard said 28 people were rescued after "Dream Keeper" went down on Sunday morning in the pristine waters at Tubbataha Reef off the western province of Palawan. The owner of the vessel, a dive master and two guests were still missing, coast guard spokesman Rear Admiral Armando Balilo said. A coast guard vessel and about 10 dive boats were searching the waters. Despite its protected status, the marine sanctuary is under constant threat from illegal fishing and poaching, according to authorities.