ANCHORAGE — A team of federal accident investigators is expected to arrive in Alaska Tuesday to try to piece together what caused a deadly midair collision between two sightseeing planes.

Four people were killed after the floatplanes carrying cruise ship tourists collided Monday near the southeast Alaska town of Ketchikan, the Coast Guard said. Two others were missing, said Petty Officer Jon-Paul Rios, a Coast Guard spokesman.

The Washington, D.C.-based investigative team from the National Transportation Safety Board is expected to arrive in Ketchikan Tuesday afternoon, agency spokesman Peter Knudson said. He said board member Jennifer Homendy also is traveling with the so-called “Go Team,” which investigates major accidents.

The floatplanes collided under unknown circumstances, Federal Aviation Administration spokesman Allen Kenitzer said in an email to The Associated Press. Floatplanes have pontoons mounted under the fuselage so they can land on water.

The passengers were from the cruise ship Royal Princess and were on sightseeing flights, one of which was operated by flightseeing company Taquan Air.

Eleven people were inside Taquan’s single-engine de Havilland Otter DHC-3 when it went down as it returned from Misty Fjords National Monument, which is part of the Tongass National Forest, the nation’s largest. Ten people were taken to a Ketchikan hospital.

All patients were in fair or good condition, according to Marty West, a spokeswoman for PeaceHealth Ketchikan Medical Center.

Three people who died were among five people aboard the second plane, a single-engine de Havilland DHC-2 Beaver, according to Coast Guard Lt. Brian Dykens. It’s unclear which plane carried the fourth victim, whose body was recovered during a Monday night search, Rios said.

Local emergency responders worked with state and federal agencies and good Samaritan vessels to help rescue and recover victims.

“It’s been a long day and the crews have been working really hard to rescue people and recover the deceased,” Deanna Thomas, a spokeswoman for the Ketchikan Gateway Borough, the local government, said Monday evening.

A spokeswoman for Taquan Air, operator of the Otter, said the company had suspended operations while federal authorities investigate the deadly crash.

“We are devastated by today’s incident and our hearts go out to our passengers and their families,” Taquan said in a statement.

Cindy Cicchetti, a passenger on the Royal Princess cruise ship told the AP that the ship captain announced that two planes were in an accident Monday. She said the ship is not leaving as scheduled and there weren’t any details as to how the accident will affect the rest of the trip.

The ship left Vancouver, British Columbia, on May 11 and is scheduled to arrive in Anchorage on Saturday.

“Our thoughts and prayers are with those who lost their lives and the families of those impacted by today’s accident. Princess Cruises is extending its full support to traveling companions of the guests involved,” Princess Cruises said in a statement.

The FAA and the National Transportation Safety Board are investigating.

Weather conditions in the area on Monday included high overcast skies with 9 mph southeast winds.

It’s not the first time a major plane crash has occurred near Ketchikan, a popular tourist destination.

In June 2015, a pilot and eight passengers died when a de Havilland DHC-3 Otter operated by Promech Air Inc. crashed into mountainous terrain about 24 miles from Ketchikan. The NTSB later determined that pilot error and lack of a formal safety program were behind the crash.