The World Health Organization issued a call to action to China Monday over HIV/AIDS as government figures said nearly half a million people are living with the disease or its precursor, with hundreds of thousands more thought to be undiagnosed.

Bernhard Schwartlaender, the World Health Organization's representative in China, wrote in an op-ed in the state-run China Daily newspaper that "there is much more China needs to do" to prevent infection and better help those living with HIV.

"Perhaps most importantly, we must eliminate stigma and discrimination towards people living with HIV, and at-risk populations such as men who have sex with men, sex workers, and injecting drug users," Schwartlaender wrote.

"I've seen some of my own colleagues in the medical profession turn patients away because they disapproved of the person's sexual orientation. That is simply unacceptable, and it has to stop," he added.

The op-ed was published on World AIDS Day, a day after the National Health and Family Planning Commission said that by the end of October, a total of 497,000 people in China had been diagnosed with HIV/AIDS since the country's first case in 1985.

The figure represents an increase from September 2013, when 434,000 people in China were known to be living with HIV/AIDS. But it was not clear whether the rise was due to an increase in infection, or more cases being diagnosed.

Another 154,000 have died from AIDS over the past three decades, the commission said.

China's National Center for AIDS/STD Control and Prevention last year estimated that as many as 810,000 people are living with HIV/AIDS in the country, including those who have not yet been diagnosed, out of a total population of 1.36 billion.

That is a far lower proportion than India, where UNAIDS says there are more two million people living with HIV, in a slighter smaller total population -- although UNAIDS does not give figures for China.

More than a quarter of a million HIV-positive people are currently on antiretroviral treatment in China, UNAIDS China director Catherine Sozi wrote in a China Daily op-ed on Saturday.

China "needs to increasingly go beyond its initial success in the roll-out of large-scale HIV programmes and focus on how to reach people who are currently falling through the cracks," she wrote.

- Discrimination lawsuit -

Sexual contact is the most common means of transmission in China, followed by mother-to-baby transmission and drug needle sharing, the Family Planning Commission said.

In the 1990s, rural parts of China -- particularly the central province of Henan -- were hit by the country's most debilitating AIDS epidemic.

It stemmed from a tainted government-backed blood donation programme and infected tens of thousands of people, including entire villages.

But now, sexual transmission accounts for more than 90 percent of infections, the official Xinhua news agency said, citing the Chinese Center for Disease Control and Prevention (CCDCP).

Gay men accounted for 25 percent of new HIV cases in the first eight months of this year, according to the CCDCP, up from 19 percent in 2012.

Discrimination against those with HIV/AIDS remains an issue at hospitals, workplaces and other establishments across the country, a factor that experts say hampers efforts to diagnose and treat the virus.

In August, two HIV-positive passengers sued a Chinese airline after staff refused to let them on board, in the country's first such lawsuit.

The two, along with an HIV-negative travelling companion, were told by Spring Airlines that their tickets had been cancelled.

Last month, the airline compensated the two HIV-positive passengers 36,000 yuan ($5,900) and the third plaintiff 15,000 yuan ($2,440), the Legal Daily newspaper reported.