Five people are dead and 10 others hospitalized after two floatplanes collided in midair on Monday near the southeast Alaska town of Ketchikan.

The pilot on each plane was flying cruise ship passengers on tours, Princess Cruises said in a statement. All five people aboard the de Havilland DHC-2 Beaver died, the cruise line confirmed. The other plane, a de Havilland Otter DHC-3, carried 11 people. 

Ten people are receiving treatment at Peace Health’s Ketchikan Medical Center.  One person is in critical condition, three are in serious condition and six people are in fair condition, Peace Health Communications Director Beverly Mayhew told USA TODAY. 

The fatalities were confirmed by Princess Cruises. One cruise ship passenger’s condition is unknown, Princess Cruises said. 

The planes crashed under unknown circumstances, said Federal Aviation Administration spokesman Allen Kenitzer.

The crash happened amid flightseeing season, the Anchorage Daily News reported, and both planes involved are frequently flown by Alaska air taxi services. 

Weather conditions at the time of the crash included high overcast skies with 9 mph southeast winds.

In 2015, a floatplane crashed into a mountain northeast of Ketchikan, killing all nine people aboard. The pilot got disoriented in cloudy weather while his company pressured him to get back to a cruise ship before it departed, federal investigators determined. 

During the eight years before the accident, Alaska recorded four fatal air-tour flight crashes involving cruise ship passengers, said Robert Sumwalt, the Acting Chairman of the National Transportation Safety Board when the investigation finished. 

Contributing: The Associated Press