The Hong Kong government was accused of "brainwashing" on Thursday after it suggested schools broadcast to students a live address by a Beijing official visiting the city.

It comes as concern grows that Chinese authorities are squeezing semi-autonomous Hong Kong's freedoms in a range of areas, from politics to media and education.

The education bureau said it had sent schools information about the seminar on Hong Kong's constitution -- known as the Basic Law -- and had invited them to broadcast it, but said it was voluntary.

Pro-democracy lawmakers said Thursday that schools now felt under pressure to show it.

"This is very, very strange. In Hong Kong, we have not had anything like this," legislator Ip Kin-yuen, who represents the education sector, told AFP.

He said the circular had suggested schools reply to the government about whether they would be broadcasting the event.

"The schools will very naturally feel the pressure from the government," he said.

Pro-democracy lawmaker Claudia Mo said it was part of Beijing's bid to re-educate Hong Kong's youth in the wake of 2014's mass Umbrella Movement protests calling for political reform and the emergence of an independence movement which wants to see a complete split from the mainland.

"(Chinese authorities) are furious that that the Hong Kong young are not patriotic," Mo said.

"It's a huge attempt at brainwashing."

The education bureau said the Basic Law seminar to be held in Hong Kong next month was part of celebrations marking 20 years since the city was handed back to China by Britain.

It will include a 50-minute speech by high-ranking Chinese official Li Fei about Hong Kong's "role and mission" under the Basic Law as a Special Administrative Region of China, according to local media.

The bureau told AFP it would "allow schools to decide whether or not to make arrangements for students to watch the live broadcast".

A proposal to introduce patriotic lessons into schools, known as "national education", was shelved in 2012 after more than 100,000 protesters rallied against it outside government offices, led by a then 15-year-old Joshua Wong.

But there are fears in the democracy camp that it is back on the agenda.

Hong Kong's Beijing-backed leader Carrie Lam announced in October that teaching Chinese history would be compulsory in secondary schools from next year.

China's education minister Chen Baosheng also said Monday that teachers in Hong Kong "need to love the country first", speaking on the sidelines of the week-long Communist Party national congress in Beijing.

In an interview with Hong Kong broadcaster RTHK, Chen added that Hong Kong needed to re-introduce national education and branded worries about brainwashing as "ignorant".