Coast Guard search and rescue crews were looking Saturday for the missing passenger, a 20-year-old Fallbrook, Calif., resident.
The man is believed to have disappeared into the water between 1 a.m. and 7 a.m. Friday while the vessel was sailing to Ketchikan, the Coast Guard said.
The Coast Guard command center in Juneau heard from the cruise line at 4 p.m. Friday that the passenger was missing.
"We searched overnight and we're still searching right now," Petty Officer 1st Class David Mosley said Saturday.
Mosley said he didn't have the man's name.
The cruise ship alerted the Coast Guard after its initial search did not find him on board.
Crews on a Jayhawk helicopter from Sitka, the 110-foot Coast Guard cutter Naushon and a 47-foot Coast Guard lifeboat all have been searching, Mosley said.
Family members reported the young man missing when he did not join them exiting the ship in Ketchikan.
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