Mao Zedong once declared: "Women hold up half the sky," but today's Chinese Communist Party is heavy with testosterone and when a new set of leaders is announced this week all are expected to be male.

About a quarter of the delegates at the party congress under way in Beijing are women. But the meeting largely rubber-stamps decisions already made behind closed doors and the higher up the echelons of real power, the more their ranks thin.

The ruling party's influential Central Committee has six percent women, the more senior 25-member Politburo has only one, Liu Yandong, and China's most powerful body the Politburo Standing Committee has never had any.

Analysts attribute women's lower representation to traditional Chinese mindsets and social structures, and a male-dominated political culture infamous for late-night drinking and mistresses.

"There's definitely this old boys' club in Chinese politics that works against women," said Leta Hong Fincher, a doctoral candidate researching gender at Tsinghua University in Beijing.

Earlier this year the state news agency Xinhua carried a report acknowledging that women faced "subcultures of Chinese officialdom like drinking alcohol" that "make it difficult for women to integrate".

"The social costs of entering politics in China are harder for women than for men," it said, citing the demands of family and standing in the eyes of society.

Some of China's most famous powerful women left terrible legacies, deepening the bias against women in politics.

Mao's wife Jiang Qing was jailed after being blamed for helping to incite the brutal 1966-76 Cultural Revolution. She later hanged herself.

The last powerful woman of imperial times, the Empress Dowager Cixi who died in 1908, is widely seen as fatally weakening China through her corrupt and despotic ways.

This hastened the country's early 20th-century collapse into civil war and anarchy.

It is not known whether Liu will retain her politburo slot and many analysts have all but ruled out her entering the topmost body. The standing committee is expected to shrink from nine to seven members, including the expected next president Xi Jinping and premier Li Keqiang.

The last female politburo member, vice premier Wu Yi who negotiated China's entry into the World Trade Organisation, was ranked No 2 on Forbes magazine's list of the world's most powerful women several times -- behind either Angela Merkel or Condoleezza Rice -- before retiring in 2008.

But she failed to break through the standing committee ceiling.

Liu has not achieved Wu's stature but has stellar political connections across the main political factions that observers believe exist in the party.

As the daughter of a former high-ranking official, she has something in common with Xi -- a so-called "princeling" who is the son of a revered Communist revolutionary.

Liu served alongside President Hu Jintao in the Communist Youth League, whose alumni form a key grouping in the party elite.

But her family was also close to Hu's predecessor Jiang Zemin, who still wields influence behind the scenes despite his retirement.

The Communist party took power in 1949 championing gender equality as part of its platform, and Fincher said it "did bring about concrete economic reforms for hundreds of millions of women".

But the emphasis on equality epitomised by Mao's comment has faded over the decades, she added.

In 2010 a survey by the state-run All Women's Federation found 62 percent of men and 55 percent of women agreed that a woman's place was in the home -- a rise of seven percent among men and four percent among women over the previous decade.

Women in cities earned only 67 percent as much as men and 56 percent as much in rural areas, the survey found.

They also lagged in labour-force participation and education level, the United Nations said in its latest report comparing the status of men and women.

Nonetheless China stands above average in global gender parity rankings, with the UN putting it in 35th place, ahead of the United States at number 47.

A 1997 Chinese government target said the legislature should be not less than 22 percent women. At 21 percent it comes slightly short, but according to the International Parliamentary Union it is a fraction above the global average, putting it in 64th slot.

Han Xiaoyun, a female congress delegate from the eastern province of Jiangsu, praised efforts to improve women's status but said they should not be chosen to attend the gathering or for other posts simply because of their gender.

"You can't say that in order to increase the proportion of women you tell qualified men to step aside," she said. "Whoever's good should be selected."