Riot police in Hong Kong have fired water cannon, tear gas and pepper spray during clashes with anti-government protesters.

The latest violent confrontations, which saw some demonstrators hurl petrol bombs at official buildings, follow weeks of pro-democracy unrest in the city.

It will fuel fears of escalating violence in the run up to China's National Day on October 1st, marking the 70th anniversary of the founding of the People's Republic.

Thousands of protesters, many clad in black with umbrellas and carrying pro-democracy posters, sang songs and chanted 'Stand With Hong Kong, Fight For Freedom' as they marched on government offices, in defiance of a police ban.

Some of them tore down and burned signs congratulating China's Communist Party ahead of the anniversary, while others sprayed graffiti and smashed windows.

An man is seen injured at Tamar Park in Hong Kong as people gathered to mark the fifth anniversary of the 'Umbrella Movement' on September 28th, 2019 | Image: Keith Tsuji/Zuma Press/PA Images

The protests were sparked in June by a planned law, now ditched, that would have allowed the extradition of suspected criminals to mainland China.

However, they have since expanded into wider demands for democracy, with many angry about what they see as creeping Chinese interference in the region.

Hong Kong returned to China's control in 1997 under the so-called "one country, two systems" policy, which guaranteed freedoms that are not enjoyed on the mainland.

Beijing has rejected claims of increasing interference in Hong Kong, and has accused foreign governments of fanning anti-China sentiment.

Hong Kong's government has already scaled down National Day celebrations in the city, cancelling an annual fireworks display and moving a reception indoors.

In recent weeks, gangs of of pro-Beijing supporters have staged counter-protests.