An explosion aboard a tourist ship off the Galapagos Islands early Friday has left six people missing and 11 injured, the Ecuadorean Navy said.

The Navy and U.S. Embassy in Quito said there were reports five Americans were among those missing from the 71-foot ship Bartolome II, which was on an eight-day cruise of the islands 600 miles west of Guayaquil, Ecuador. An Ecuadorean crew member was also reported missing.The remote islands, visited by the explorer Charles Darwin, are a popular tourist site replete with rare birds, fish and flora.

Authorities said it was believed a gas leak caused the explosion on board the Nuevo Mundo line, which is based in this Andean capital. The boat caught fire and quickly sank, according to the reports.