Alledgedly somewhere around 10,000 BC a giant alien space ship would have crashed in the Himalayas, in a region that is now on the Chinese - Tibetan border. Descendants of the crash survivors would still live there in an isolated tribe. They would be called the Dropas, are said to be human-looking, yet would on average only be 3 to 4 feet tall.
Other alien 'immigrants' are the Norcans and the Janosians.