(CNN) At least four people are dead after two floatplanes carrying cruise ship passengers collided in flight near Ketchikan, Alaska, according to the US Coast Guard.

The passengers on both planes were guests on a Princess Cruises ship, the Royal Princess , which is on a seven-day trip.

The Coast Guard, which is leading an investigation into the Monday afternoon crash, told CNN it is still looking for two people.

Ten people were rescued and are receiving medical care following the collision between a Beaver floatplane and an Otter floatplane, the Coast Guard said Tuesday in a statement.

A floatplane is an aircraft with pontoons or floats that allow it to land on water.

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