On Wednesday, both Chinese President Hu Jintao and US President Barack Obama recalled in their speeches the days when China and the United States broke off their estrangement and started to engage in exchanges and improve mutual understanding despite their differences in ideology and social systems.

While Obama quoted late Chinese leader Deng Xiaoping's comment that there are still great possibilities for cooperation between the two countries, Hu went back 40 years to recollect how former US president Richard Nixon, along with his then national security advisor Henry Kissinger, made the ice-breaking visit and started a relationship that has changed the world.

Since then, China-US relations have weathered many trials and tribulations with seven US presidents and four generations of Chinese leadership.

Nixon is long-gone. But I saw the familiar faces of Kissinger and some of his successors, George Shultz, Madeleine Albright and Colin Powell at Wednesday's lunch, jointly hosted by Vice-President Joe Biden and US Secretary of State Hillary Clinton. They have all experienced the rollercoaster ride of China-US bilateral relations, as ties expanded and the two countries become more and more interdependent.

Things have changed in the last 30 years.

First of all, China has changed.

While we waited for the dignitaries to arrive for the lunch at the US State Department, Larry Downing, a Reuter's photographer, recalled the few days he spent in Beijing in 1978, covering the then US vice-president Walter Mondale's visit.

He said he remembered staying at the Minzu Hotel, "the only tall building" on that section of Chang'an avenue. "The city was almost flat, and the streets were filled with bicycles," he said. "I could even hear the sounds of the bicycles rolling.

"That was real China," said the photographer, who went to Beijing to cover the visit by US Defense Secretary Robert Gates early this month ahead of Chinese president's state visit in the US.

"With all the tall buildings and so many cars in the streets, China is not much like China any more," he told me.

Indeed, to many people, China has become a different country to the one more than 30 years ago.

Whatever misgivings people may have about China's transformation, China is now highlighted in the US media as the country that produces more automobiles than the US, that has overtaken Germany to become the world's largest exporter, that has surpassed Japan to become the second largest economy in the world, and one that is upgrading its military capability.