Dive teams are searching for the missing pair in the icy cold waters of a southeast Alaska inlet on Tuesday. The other passenger is a Canadian.
The Coast Guard confirmed there were four fatalities in the collision on Monday afternoon near Ketchikan, a popular destination for cruise ships in Alaska.
Ten people, all Americans, were injured. The missing passengers were from Canada and Australia, Princess Cruises said.
The Royal Princess, which can carry up to 3600 people, was among four city-sized cruise ships in the tiny coastal community on Monday.
A popular activity is “flightseeing” in Misty Fjords National Monument to view the lakes, snow-capped peaks and glacier valleys in the wilderness area.
The larger plane, a de Havilland Otter DHC-3 with 10 passengers and the pilot, was returning from Misty Fjord when it collided with another sightseeing plane carrying four passengers from the same cruise ship and a pilot.
The cause of the crash in relatively good weather, high overcast skies with light southeast winds was not known.
The crash occurred about 13 kilometres from Ketchikan, near George Inlet. The planes came down about two kilometres apart with some of the debris field on land.
The smaller plane, a de Havilland DHC-2 Beaver, was partially submerged in the shore of George Inlet after the single-engine plane overturned and hit some trees before crashing, according to Coast Guard Lt Brian Dykens. The larger Otter landed in water and sank, he said.
Investigators from the National Transportation Safety Board were due to arrive later on Tuesday.
Three others who died were among the five people aboard the Beaver, according to Dykens.
Princess Cruises in its release said two passengers and the pilot were among those killed in this plane.
Canadian officials said on Tuesday one of its citizens was among the dead. The Beaver appears to have broken apart in midair, according to Jerry Kiffer, duty incident commander of the Ketchikan Volunteer Rescue Squad.
He said the plane’s tail and section of the fuselage were 275m from the aircraft’s floats, which landed near shore.
After the crash, the 10 injured passengers were initially taken to a hospital in Ketchikan. Four patients were later transferred to Harborview Medical Center in Seattle, suffering various broken bones, spokeswoman Susan Gregg said.
The Royal Princess left Vancouver, British Columbia, on May 11 and was scheduled to arrive in Anchorage on Saturday.
“We are extending our full support to the investigating authorities as well as the travelling companions of the guests involved,” the company said in a statement.