SAN FRANCISCO -- More than three dozen vacationers aboard the Crown Princess have become ill this week during a cruise along the California coast that stopped in San Francisco on Monday.

A statement from Princess Cruises says 37 passengers -- about one percent of the ship's passengers -- have been reported ill, and likely are suffering from norovirus. The highly contagious virus can be spread from person to person, from contaminated food or water, or by touching contaminated surfaces. It causes stomach pain, nausea and diarrhea.

Princess Cruises said after discovering the outbreak it "immediately initiated additional enhanced sanitation procedures to interrupt the person-to-person spread of this virus."

The weeklong cruise departed Los Angeles on Saturday with stops that include San Francisco. A total of 3,161 passengers and 1,176 crews members are on board, the statement said.

David DeBolt covers breaking news. Contact him in Richmond at 510-262-2728. Follow him at Twitter.com/daviddebolt.