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 when the floatplanes carrying cruise ship tourists collided Monday near the southeast Alaska town of Ketchikan, the Coast Guard said.

Two others were missing, according to Petty Officer Jon-Paul Rios, a Coast Guard spokesman.

Princess Cruises said one of the planes was flying a shore excursion sold through its cruise line, and that it was carrying ten guests and a pilot. The second plane, an independent flight tour, was carrying four people from the cruise ship Royal Princess as well as a pilot, it said.

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Multiple people were rescued, according to Princess Cruises and the Coast Guard.

Both aircraft plunged into waters below, where they are submerged, a source familiar with the situation told CBS News. Investigators believe one came to rest in a lake, the other in the ocean. It was unclear how far apart they are.

A 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.

Emergency response crews transport an injured passenger to an ambulance at the George Inlet Lodge docks, Monday, May 13, 2019, in Ketchikan, Alaska. Dustin Safranek/Ketchikan Daily News via AP

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.

Map shows location of sightseeing plane collision near Ketchikan, Alaska on May 13, 2019 Google Maps

A spokeswoman for Taquan Air, operator of one of the planes, 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 the ship was not leaving as scheduled and there weren't any details on how the accident will affect the rest of the trip. The ship left Vancouver, British Columbia, on May 11 and was 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.

It wasn't the first major plane crash 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.

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