That too was also considered optimistic at the time but the financial crisis has hit the US hard and might now even be considered a conservative estimate.

Since then, China has emerged in pole position when it overtook Japan to become the world's second-largest economy in February 2011.

Hu, who is a professor of economics at China's elite Tsinghua University and the author of no fewer than 60 books, is raising the stakes with his own prediction, going further than any forecast either in China or overseas.

He believes China will be driven forward by what he terms five engines: accelerating industrialization, its major role in a new globalized world, its dominance in information technology, the rapid modernization of its infrastructure in areas such as electricity supply and high-speed railways, and the growing internationalization of its own economy.

He points out that China's workforce of 780 million is five times larger than the US' 153 million and that it now devotes 3 million person-years to research and development, twice the deployment of the US, both adding to its growth momentum.

Goolam Ballim, group chief economist of Standard Bank Group based in Johannesburg, said it is not inconceivable the Chinese economy will be double the size of the US' by 2030. His own forecast is that it will achieve that position by at least 2040.

"To some extent it is like the old adage that it is easier to make your second million dollars than your first. Once China has caught up with the United States in terms of GDP, it will be easier for it to progress from there to become twice as big."