Thousands of stroller-pushing Hong Kong parents and activists Sunday protested a plan to introduce national education lessons, slamming it as a bid to brainwash children with Chinese propaganda.

The government has said the subject is important to foster a sense of national pride and belonging, although its bid to start introducing the subject in September and make it compulsory in 2015 has sparked a public outcry.

Organisers said 90,000 demonstrators took part in the noisy protest, which was led by parents and young students. Police put the figure much lower at 32,000.

"As a parent, I'm very angry, this is a blatant brainwashing," mother-of-three Sandra Wong said as she marched in the sweltering heat accompanied by her husband and pushing her two-year-old daughter in a stroller.

"The curriculum only paints a rosy picture about the Communist Party... This is just an attempt to introduce the mainland agenda in Hong Kong schools," she said.

Sunday's protest underscored rising anti-Beijing sentiments, coming weeks after the city's biggest demonstration in nearly a decade, as new leader Leung Chun-ying was sworn in before Chinese President Hu Jintao.

A poll released by the University of Hong Kong last month showed the number of people in the former British colony identifying themselves as citizens of China had plunged to a 13-year-low. More identified themselves as Hong Kongers.

The government has rejected the brainwashing claims and vowed to push ahead with the plan, although it announced the formation of a special committee to monitor the implementation of the subject following the mass protest.

The committee will ensure the subject is taught in a way "to educate our students to have independent thinking, to be able to analyse situations and come to an objective judgement", Chief Secretary Carrie Lam told reporters.

Under the proposal, students would take 50 hours of lessons a year focusing on "building national harmony, identity and unity among individuals". There would be no exams.

"There is nothing wrong with national education but it shouldn't be done in a biased way," high school student Shirley Cheung said at the protest.

"Currently the curriculum makes no mention about issues like the Tiananmen Square crackdown or who is (Chinese dissident) Ai Weiwei, so we are not convinced it can encourage independent thinking," the 17-year-old added.

The protest came after a teaching booklet called "The China Model", which heavily praised China's one-party system, was sent to local schools in recent weeks, further fuelling debates over the lessons.

The plan to introduce national education has been on the government's agenda for years but the fresh push came weeks after the new government led by Leung, seen as pro-Beijing, took office.

Hong Kong returned to China in 1997 as a semi-autonomous territory with its own political and legal system that guarantees civil liberties not seen on the mainland, including freedom of speech and association.

Anti-Beijing protests are a regular fixture in the regional financial centre of seven million people.