Job ads posted by Alibaba Group Holding Ltd, Baidu Inc and Tencent Holdings Ltd were among those that deterred female applicants or objectified women, said Human Rights Watch in a report released on Monday.
In many of the adverts, prospective employers boasted of "beautiful girls" at their workplace as a selling point for new employees, while others included specific height, appearance and temperament requirements for women that were unrelated to the roles.
"We have investigated these incidents and are making immediate changes. We are sorry they occurred and we will take swift action to ensure they do not happen again," Tencent said in a statement.
An Alibaba spokeswoman said the company "will conduct stricter reviews of the recruiting advertisements to ensure compliance with our policy."
A Baidu spokeswoman said the postings were "isolated instances".
The report comes amid a larger Chinese movement against gender-based discrimination and harassment, buoyed by the global #MeToo movement, which has since been heavily censored online in the country.
The #MeToo movement began last year as victims of discrimination and sexual harassment took to social media to share their stories under the hashtag #MeToo. Silicon Valley firms have since been accused of discriminatory behaviour, turning the focus on tech worldwide.
Human Rights Watch, which analysed 36,000 Chinese job advertisements largely posted since 2013, also criticized adverts for government roles, construction workers and kindergarten teachers.
Reuters sent a fax seeking comment to the Ministry of Public Security, a bureau mentioned in the report, but did not receive a response.
Some firms looked to avoid scrutiny of their practices, including using code words to show a male preference, Human Rights Watch said. One used the Chinese word for south, "nan", which in Chinese has the same pronunciation as the word for "man", it said.
It added discriminatory hiring behaviour was a key issue behind the relatively low numbers of women in the workforce and growing gender disparity over urban pay.
Chinese laws ban discrimination based on gender, but "enforcement is low and Chinese authorities rarely proactively investigate companies that repeatedly violate relevant laws," Human Rights Watch said in the report.
The country's #MeToo movement has, however, been gaining momentum on university campuses since late last year, and several schools have cut ties with professors amid claims of harassment and assault dating back decades.
The Human Rights Watch report received a muted response on Chinese social media on Tuesday, with almost no posts commenting on the issue on popular microblog platforms such as Alibaba-backed Weibo or Tencent's mobile chat app WeChat.
Chinese social media firms are often required to censor civil rights discussions, including previous Human Rights Watch findings and posts related to the #MeToo movement.
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