The EP-3 intelligence aircraft of U.S. Navy. [File photo]

In the past, American aircraft would regularly enter Chinese airspace, as many U.S. EP-3 intelligence aircraft were based in Japan. The Hainan Island incident in 2001 may be the most well-known encounter between the U.S. and China. On April 1, 2001, a U.S. Navy EP-3 intelligence aircraft flying close to Chinese airspace was intercepted by two PLAN J-8 interceptor fighter aircrafts, resulting in a collision between the U.S. and Chinese fighters. One Chinese pilot was killed in the incident.

China's computer and telecommunications systems also fall within the scope of U.S. spying programs. The Office of Tailored Access Operations (TAO), a body within the U.S. National Security Agency (NSA), is tasked with gaining access to foreign computer systems and according to reports, it has been successfully penetrating Chinese computer and telecommunications systems for almost 15 years, gathering the best and most reliable information about what is going on in China.

Speaking during a confirmation hearing for his new role as director of U.S. National Intelligence in 2005, John Negroponte said: "Our children and grandchildren are going to live in a world where China will be a very strong and powerful player on the world scene."

He told a Senate committee: "In terms of longer-term intelligence analysis, I think it's very important to follow countries such as China, analyze them well and carefully so that we understand the longer-term implications that a country like that has for our foreign policy."