A tourist submarine, Sinbad, went down off Egypt’s Red Sea coast in the early hours of Thursday, killing at least six people and injuring nine. At least 29 people were rescued from the sub, and four critically wounded individuals were taken to nearby hospitals, BBC said.

The Sinbad submarine, one of several that have been operating in the Hurghada area for years, carried 40 individuals when the accident occurred. The company that owns the vessel says it has two of the world’s only “14 real recreational submarines.”

As the Sindbad Submarines website says, the submarine takes tourists 25 meters (82 feet) under the surface to see “500 meters of coral reef and its marine residents.” The submarine has ’44 passenger seats—two pilots’ seats and a large round viewing window for each passenger.”