The conference version of the study, available at the bank's Web site, says some estimates of the physical and economic cost of pollution have been omitted because of uncertainties about calculation methods and their application.

However, the report goes on to estimate the health costs from premature deaths associated with outdoor air pollution at 394 billion yuan (US$51.8 billion). With each life valued at 1 million yuan, that works out at a death toll of 394,000.

The study puts the cost of deaths from diarrhoea and cancer caused by drinking polluted water at 66 billion yuan, pointing to 66,000 premature deaths a year.

China-watchers said it was standard practice in research projects conducted with the government for both sides to have a veto over the conclusions.

The World Bank said the final report would be out soon.

"Consistent with the World Bank's approach to this type of joint research project, the findings of the report are being discussed with the government. The conference version of the report did not include some of the issues that are still under discussion," the bank's Beijing office said in a statement.

An economist in Beijing said the study's estimate of premature deaths from airborne pollution, although shocking, was broadly in line with earlier published World Bank research and with recent findings by Chinese academics.

The World Bank is also concerned by indoor air pollution, principally breathing in fumes from coal-burning stoves and cooking oil. Its experts estimate that as many as 300,000 Chinese a year die prematurely in this way.

China, home to some of the world's 20 most polluted cities, is redoubling its efforts to clean up the environment.

The authorities are closing down dirty industrial plants, raising car fuel-efficiency standards and tweaking taxes to discourage energy-intensive production. China on Sunday also introduced higher drinking water standards.