Democracy protesters took part in the largest mass rally through Hong Kong's streets in months on Sunday in a forceful display of support for the movement, with a leading activist warning the city's pro-Beijing leaders they had a "last chance" to end the political crisis.

Organisers estimated some 800,000 people snaked for hours through the financial hub's main island as the protests marked six months, a vivid illustration of the hostility that still seethes towards the government after half a year of unrest.

The city's police force, which historically gives lower crowd turnout figures, told local media 183,000 people attended at the peak, still one of their highest estimates in months.

The rally received rare police permission and came two weeks after pro-establishment parties got a drubbing in local elections, shattering government claims that a "silent majority" opposed the protests.

As night fell the crowds switched on their mobile phone torches, creating a glittering carpet of lights that stretched far into the distance, their chants bouncing off the towering skyscrapers above.

Many of the black-clad attendees voiced anger and frustration that chief executive Carrie Lam and Beijing have ruled out any further concessions despite the landslide election defeat.

"No matter how we express our views, through peacefully marching, through civilised elections, the government won't listen," said a 50-year-old protester, who gave his surname Wong. "It only follows orders from the Chinese Communist Party."

"I don't know how long the fight will be," added another protester, who gave his first name as Kelvin. "So far I can't see the end but we won't back down."

Cantonese popstar Denise Ho, whose music is blacklisted on the Chinese mainland, tweeted a video of the huge crowds with the caption: "Here's your majority Carrie Lam".

Semi-autonomous Hong Kong has been battered by increasingly violent demonstrations in the starkest challenge the city has presented to Beijing since its 1997 handover from Britain.

Millions have marched in protests fuelled by years of growing fears that authoritarian China is stamping out the city's liberties.

The last fortnight has seen a marked drop in violence and vandalism after the landslide win by pro-democracy candidates.

Copyright Agence France-Presse, 2019