China's confirmed cases of HIV rose more than 50 percent in the past year but poor monitoring and official obstruction still obscure the real scale of the AIDS epidemic, the country's top AIDS official said on Monday.

The number of Chinese medically diagnosed with the HIV virus, which leads to AIDS, grew to 135,630 by the end of September, Wang Longde, director of the State Council AIDS Prevention and Treatment Work Committee, told a conference of Chinese health officials ahead of World AIDS Day on Thursday.

By the end of September last year, China had 89,067 HIV cases.

But China's vast size and dilapidated health system mean that only a fraction of HIV-positive people are officially diagnosed with the virus, and even fewer of them receive medical treatment for full-blown AIDS.

Vice Premier Wu Yi said that the gap between reported statistics and the real scale of the epidemic threatened to undermine the country's fight against AIDS.

"If we can't do the maximum to locate carriers and sufferers, then we can't do the maximum to implement prevention and treatment measures," Wu said. She said the reported HIV cases probably represented 16.1 percent of the real number -- which would give China an estimated 840,000 cases of the disease.

Wang said local officials continued to cover up cases of HIV infection, fearful that acknowledging the epidemic would harm economic growth and promotion prospects.

"Some localities fear that reporting a rise in reported cases will damage their political standing and local economic development, and they are unwilling to expand testing. And certain areas won't even truthfully report cases," Wang said.

The United Nations Joint Programme on HIV/AIDS has said that number could be anywhere between 430,000 and 1,500,000, and some international groups and Chinese AIDS activists put the figure in the millions.

China recorded its first outbreak of AIDS in 1989. Last year, between 21,000 and 75,000 Chinese died of AIDS, according to the United Nations -- many of them poor, rural residents who died without treatment or even diagnosis.

Officials at Monday's meeting said that as HIV was spreading increasingly through sexual contact, especially prostitution, through intravenous drug use, and from mothers to babies, the virus was more likely to spread throughout the larger population and China would face difficulty containing it.

Wu said that to hold back AIDS, China must expand needle exchange programmes and methadone-based detoxification services for drug users and condom distribution to prostitutes and men who have sex with men.

The infection rate among prostitutes rose from 2 in 10,000 in 1996 to 93 in 10,000 in 2004, Wang said. And in "high-prevalence" areas, such as the rural central province of Henan, 0.26 percent of pregnant women were found to have HIV.

But Wu said local officials wary of being seen as condoning drugs and prostitution were holding back these policies.

"Many of these measures are stuck at the trial stage, and their depth and breadth aren't enough," she said. "There is even obstruction of measures to intervene in these high-risk behaviours, and this has held back prevention and treatment."

During the 1990s, many Chinese -- especially in Henan -- contracted the virus through contaminated blood transfusions. This was a time when cash-hungry peasants sold their blood to professional blood buyers, often accredited by local health agencies or the military.

The blood was pooled, plasma extracted for medical use and the remainder returned to the donors in pooled batches, meaning that one infected person passed the disease to others.

But now 40.8 percent of the confirmed cases were infected through intravenous drug injections, 9.0 percent through sexual transmission, 23.0 through blood selling, and 23.4 percent were of uncertain origin, Wang said.

Wu said these shifting patterns of transmission exposed growing numbers of Chinese to the risk of infection. "HIV in China remains a low-level epidemic, but among certain groups and regions it's become a high-level one, and it's steadily spreading from high-risk groups to the general population," she said.