The warning was sent out by the U.S. Consulate in Guangzhou and was dated Sunday. It didn't give any information about the source of the threat or other details.
"The United States government has received credible information that a terrorist threat may exist against official U.S. government facilities in Guangzhou," the warning said.
"This threat also may exist for places where Americans are known to congregate or visit, including clubs, restaurants, places of worship, schools or outdoor recreation events."
It told Americans in southern China to "be aware of their surroundings and remain alert to possible threats."
The warning was sent by e-mail to Americans registered with the Guangzhou Consulate and to those in nearby Hong Kong, said Susan Stevenson, a spokeswoman for the Hong Kong Consulate.
The warning follows a similar alert last week from the U.S. Embassy in Beijing, which announced the possibility of a terror threat aimed at luxury hotels in the Chinese capital. The embassy retracted that warning a day later, saying Chinese authorities concluded the source of the information wasn't credible.