At least five Russian tourists, including two children, were killed Thursday when a submarine sank off Egypt’s Red Sea coast, according to Russian officials in the region.

The submarine was making a routine excursion to observe coral reefs, according to a statement from the Russian embassy in Egypt. The vessel had 45 passengers — all Russian tourists, the embassy said. The number of crew members was not specified.

Emergency crews on the coast have rescued at least 38 Russians, reports the Russian news agency RIA Novosti. Of those, 14 have been hospitalized and 24 have been returned to their hotels, according to RIA Novosti. Several Egyptians and Indians were also hospitalized, the agency reported.

The cause is still unclear. The submarine sank about half a mile off the shore of the Egyptian resort town of Hurghada at 10 a.m. local time. The vessel, called Sindbad, was chartered by a resort of the same name.

A website for the Sindbad submarine experience boasts that “there are only 14 real recreational submarines in the world,” and that Sindbad operates two of them. Trips last three hours and reach a maximum depth of about 82 feet.