Authorities said the Hong Kong National Party (HKNP) posed a threat to national security.

Under the so-called "one country, two systems" formula, Hong Kong enjoys a high degree of autonomy and certain freedoms not available in China.

The ban comes amid growing concerns those freedoms are being eroded under pressure from Beijing.

It is the first time that the territory has banned a political party since it was returned to China from the UK.

How is the ban justified?

A colonial-era law allows the government to ban groups "in the interests of national security, public order or the protection of the rights and freedoms of others".

The city's Secretary for Security John Lee said the group had spread "hatred and discrimination against mainland Chinese".

The HKNP is a small fringe party and there is very little support within Hong Kong for the independence movement.

But the move to outlaw the party has given the group and its leader Andy Chan international prominence.

Hong Kong's Foreign Correspondent Club hosted Andy Chan despite protest from Beijing

In August, he gave a controversial speech at the city's Foreign Correspondent Club (FCC), sparking criticism from Beijing and pressure for the FCC to cancel the talk.

A former British colony, Hong Kong was returned to China in 1997. But due to the "one country, two systems" formula, Beijing agreed to give the region a great deal of autonomy and to preserve its economic and social systems for 50 years.

Why is this important for China?

China is extremely - and increasingly - sensitive about what it says are questions of national sovereignty.

Beijing's main focus is Hong Kong and the self-ruling island of Taiwan. In Taiwan's case, China's position is straightforward: Beijing sees Taiwan as a breakaway province that rightfully belongs to the mainland.

In the case of Hong Kong, the situation is blurry. The city is part of China but its special status and freedoms can be seen as indirectly undermining Beijing's tough hand on the mainland.