Members of a pro-government group gather outside the Foreign Correspondents' Club in Hong Kong to protest a scheduled talk by pro-independence advocate Andy Chan Ho-tin.

Mainland China and local authorities are calling for the cancellation of a scheduled speech from a member of a pro-independence Hong Kong political party, raising concerns about the state of free speech in the city.

The Hong Kong Foreign Correspondents' Club has planned to host Andy Chan Ho-tin, leader of the Hong Kong National Party, on Tuesday of next week for a talk entitled "A Politically Incorrect Guide to Hong Kong under Chinese Rule."

Chan's party advocates independence for Hong Kong, a semi-autonomous region of China that was a British colony until 1997. The local government is considering a police request to ban the party on national security grounds.

Under a Sino-British accord, Hong Kong kept its legal system, currency and civic freedoms, famously guaranteed for 50 years under the "one country, two systems" formula.

Hong Kong is a major global financial and trade center of about 7.4 million people and its combination of low regulation, free speech and rule of law have contributed to the city as a favored center for international banks and multinational companies.

But scholars and rights organizations say Hong Kong's autonomy has eroded over the past two decades as China increasingly exerts pressure on local authorities to curtail democratic aspirations.

Hong Kong was rocked in 2014 by street protests calling for more democracy, with local authorities eventually taking a hard line as Beijing watched closely.

The central government has come down hard on any calls for independence which, while rare, are seen as a red line over which authorities will never compromise.

The Chinese government has called for Chan's invitation to be withdrawn.

"We are firmly against the attempt of any external forces to provide venue to the advocates for 'Hong Kong independence' to spread their nonsense," the foreign ministry's office in Hong Kong said in a statement on its website.