At least 30 people died after their boat sank off the Indian Ocean archipelago of Comoros, a rescue official said Tuesday. "At the moment the death toll stands at 30 and 50 survivors," Mouigni Daho, the head of the centre for rescue operations and civilian protection, told AFP. It was not exactly clear what caused the accident, but a Red Crescent official said the vessel, Madjiriha, was believed to have suffered an engine failure and hit a huge rock as it tried to move towards the coast. The accident occurred Monday night to the south of the Comoros' main island of Grande Comore where the boat had left for the archipelago's other island of Anjouan. Red Crescent rescue coordinator Arfachad Salim said the death toll could increase. "We cannot rule out that passengers are still trapped inside the boat," said Salim, who earlier explained that they estimated that more than 100 people were on the boat. Those with serious injuries were rushed to the main hospital in the capital Moroni, while others were treated in local health centres. Search operations were under way and divers were to inspect the wreckage later on Tuesday, while the captain, who also survived the accident, was expected to give clarifications, Salim said. Boat accidents are common in the tiny archipelago, especially those carrying migrants from the impoverished isles to the French island of Mayotte. Geographically, Comoros is made up of four islands of Grande Comore, Anjouan, Moheli and Mayotte. But Mayotte voted to remain part of the islands' colonial master France and is economically better off than its neighbours.