Contrary to popular belief, if you are in the United States, you cannot dig a hole through the center of the Earth and end up in China. In fact, with the exception of three small areas in the 48 contiguous states, you would end up in the middle of the ocean. The three exceptions are Carville, Colorado, near U.S. Route 109, which is directly opposite to a small island near Antarctica; La Junta, Colorado, which lies opposite to Île Amsterdam; and part of Shelby, Montana, which is opposite to the Kerguelen Islands, also known as the Desolation Islands because of their extreme remoteness. Hawaii and Alaska also have land at their opposite points: if you were to dig through the center of the Earth from Hawaii, you'd end up in Botswana or Namibia; if you dug through in Alaska, you'd end up in Antarctica.
More facts about digging through the Earth: