WASHINGTON, Oct. 4 (Xinhua) -- Former U.S. Secretary of State Henry Kissinger has congratulated the Chinese people on their "unbelievable accomplishments" over the past 60 years, saying that China's modern transformation is an "extraordinary historic event."

"If anyone had predicted to me in 1971 what China looks like in2009, I would have thought he was dreaming... but you have made a reality out of these dreams, " Kissinger said in a recent interview with Xinhua at his New York office on the 60th anniversary of the founding of the People's Republic of China, which falls on Oct. 1.

    Kissinger, who helped pave the way for the normalization of U.S.-China relations in 1979, said the 30-year-old bilateral relationship has grown remarkably.

    "In all the years that I have seen the Sino-American relationship, I have never seen such warmth on both sides," he said.

    Kissinger said now is time for the two countries to "rebalance" their respective roles in the relationship due to their changed national power in a global context.

    "The world that originally saw the Chinese-American relationship was different from the world today," he said. "In that sense, both sides really have to rebalance the relationship."

    The United States needs to take into account the growing role China is playing, while China needs to adjust itself to assume bigger responsibilities, Kissinger said.

    Meanwhile, cooperation remains a key solution to the global challenges, he added.

    "The United States and China should have a very close relationship," Kissinger said. "They should constantly exchange ideas, so when they go into an international forum like the G20, they have parallel positions and can work together."

    Energy and environment remain two major long-term challenges the world has to face, while nations worldwide have yet to coordinate in the globalized economic system, he said.

    It is "the imperative of our time" that China and the United States cooperate on these global challenges, he said.

    The Group of 20, or G20, should become an inclusive platform for international political and economic affairs for "the next few decades," he noted.