China will overtake the United States economically within six years, an official research institute predicts, and go on to become the world's most important country in three decades more, state media said Wednesday.

The findings came from the Nation's Health Report issued by the Chinese Academy of Sciences, the Global Times said, without giving details of the criteria used for the prediction.

China's economy would be larger than that of the US by 2019, it cited the document as saying, and China's "international status" would exceed that of the US by 2049, the 100th anniversary of the founding of the People's Republic.

"National health" was defined as a country's "overall conditions... using resource sufficiency and wealth distribution as the major criteria", the Global Times said, but did not go into specifics.

China ranked as the 11th "healthiest" country out of some 100 nations, it said, just behind Costa Rica, with Sweden in top position.

The official Xinhua news agency said China was given a national health status of "up to standard", though the US, Japan and Britain were deemed "health deficient".

The report could not immediately be independently obtained from the Chinese Academy of Sciences.

China's stunning economic growth rates, increases in military spending and overlapping security interests in the Asia-Pacific region with the US have sparked concerns the countries could find themselves increasingly at odds in coming decades as they jockey for global influence.

But the Global Times, which has close ties to China's ruling Communist Party, said the document's findings were seen by some as overly nationalistic.

"The report is indicative of an anti-US sentiment in Chinese society," Fang Zhouzi, described as a prominent whistleblower on academic fraud, told the paper.

"It casts the US as a potential threat and links the goals of China's national revival to surpassing the US," he added.

Decades of economic reform and openness to foreign investment have propelled China from a poor, overwhelmingly agricultural country to become the world's second-largest economy behind the US.

International analysts widely expect China's economy, given its high growth rates, to overtake the US in terms of gross domestic product, or total size, some time in the first half of this century, though differ on exact timing and criteria.

But they also see the US as likely to remain wealthier on a per capita basis given China's huge population of 1.3 billion, with that of the US currently at about 315 million.