The floatplanes carrying cruise ship tourists collided Monday near the southeast Alaska town of Ketchikan and 10 people were rescued.
Main image: Emergency response crews transport an injured passenger to an ambulance at the George Inlet Lodge docks, Monday, May 13, 2019, in Ketchikan, Alaska.
"All of us at Princess Cruises are deeply saddened by this tragic news and we are extending our full support to the investigating authorities as well as the travelling companions of the guests involved", company spokesman Brian O'Connor said in a statement.
The ship was on a seven-day cruise that ends in Anchorage, Alaska, on Saturday.
The death toll was initially reported as four, with two people missing. Multiple other passengers were injured.
Ten people have been admitted to PeaceHealth Ketchikan Medical Center, a spokeswoman with the hospital, Mischa Chernick, told the Anchorage Daily News.
The Coast Guard is searching with the cutter Bailey Barco, an Air Station Sitka MH-60 Jayhawk helicopter crew, a HC-130 from Kodiak is flying in relief crews from Sitka and two Station Ketchikan 45-foot Response Boat-Mediums.
It is unclear which plane carried the fourth victim.
She said the ship was not leaving as scheduled and there weren't any details as to how the accident will affect the rest of the trip.
The larger plane was operated by Taquan Air of Ketchikan and passengers booked the flights through the cruise ship as an excursion.
Taquan Air, the company which operated the De Havilland Otter plane, said in a statement that it has suspended all flights.
"We are devastated. and our hearts go out to our passengers and their families", it said in a statement.
"Our focus is on assisting these passengers, the pilot, our staff, their families and loved ones, and first responders."
A San Diego resident has been identified as one of six people killed in a mid-air collision in Alaska earlier this week.
Three people who died were among the five on board the second plane, a single-engine de Havilland DHC-2 Beaver, according to the USA coastguard.
A preliminary report by the ATSB found there were no obvious mechanical defects or fuel contamination on the aircraft, which was up-to-date with maintenance checks and flown by a well-qualified pilot, Canadian-born Gareth Morgan, 44.
Weather in the area where the crash happened Monday included high overcast skies with southeast winds gusting at 14 kilometres per hour.
The National Transportation Safety Board said it was launching a "Go Team" to investigate the cause of the accident.
A plane with cruise line passengers crashed into a mountain while returning from the Misty Fjords National Monument, killing all eight passengers and the pilot.