Formal:
* 您好，欢迎来到中国。 (Nín hǎo, huānyíng lái dào Zhōngguó.)
* This is the most polite and formal way to say it. It uses the honorific "nín" for "you".
Informal:
* 你好，欢迎来中国。 (Nǐ hǎo, huānyíng lái Zhōngguó.)
* This is a more casual way to say it, using "nǐ" for "you".
More informal (especially with friends):
* 欢迎来中国！ (Huānyíng lái Zhōngguó!)
* This is a shortened, more casual way to say it.
Note:
* In all of these phrases, "欢迎来到" (huānyíng lái dào) can be shortened to "欢迎" (huānyíng), which still means "welcome".
* You can also replace "中国" (Zhōngguó) with the specific city or region you're in, for example, "欢迎来到北京" (Huānyíng lái dào Běijīng) for "Welcome to Beijing".