"to drug a man unconscious and ship him as a sailor," 1854, American English, from the practice of kidnapping to fill the crews of ships making extended voyages, such as to the Chinese seaport of Shanghai.
Chinese seaport, literally "by the sea," from Shang "on, above" + hai "sea." In 19c., a long-legged breed of hens, supposed to have come from there; hence U.S. slang senses relating to long, tall persons or things.
Note: Shanghai is the most populous city in Asia.
Note: It is one of the world's great seaports.
Note: Opened to foreign trade by the Treaty of Nanking in 1842, Shanghai became a treaty port administered by Britain, the United States, and France until World War II.