At least 16 people are missing after an Egyptian yacht carrying international tourists sank in the Red Sea on Monday.

Forty-four people, including 13 crew members and 31 tourists, were aboard the Sea Story when it sank near Marsa Alam, a resort town in southeastern Egypt. The ship was carrying tourists for a multi-day diving trip.

Egyptian media outlet Al-Dostor reported that two American tourists were on board, but it is unclear if they are among those missing. Authorities were alerted to the incident at around 5:30 a.m. on Monday.

“Immediately, [authorities] informed the Naval Base and the Armed Forces, where search and rescue teams began operations using a helicopter and a marine unit moving from Bernice Harbor towards the rescue site,” the Red Sea Governorate explained in a Facebook post.

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“The [Egyptian] Control Center and Operations Room continue to coordinate and follow up around the clock to ensure all necessary actions are taken and situation is reassured.”

The search is ongoing and the number of deaths have not been officially announced.

Egyptian officials reported that 28 people have been rescued. Among that group, minor injuries like scrapes and bruising were reported, but no victims were hospitalized.

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The group of missing people includes 12 foreign nationals. The ship carried citizens of the U.S., Belgium, Spain and Germany, along with citizens of the United Kingdom, China, Finland, Ireland, Poland, Slovakia and Switzerland.

While the cause of the sinking has not been determined, officials believe that a massive wave capsized it. The vessel sank within five to seven minutes.

“Some passengers were in their cabins, which is why they were unable to escape,” Red Sea Governor Amr Hanafi said in the statement.

Authorities are actively investigating the incident. No additional information is known at this time.

Reuters contributed to this report.