Dressed in black and toting umbrellas and yellow placards, more than 1,000 people turned up on Wednesday night in London's West End in a show of support for Hong Kong's ongoing pro-democracy campaign.

One of among 64 similar protests planned in various cities around the world, the London event saw protesters occupy half of Portland Place as they sat on the road across from the Chinese Embassy on China's National Day.

Chanting pro-democracy slogans, the participants - mostly students and young professionals from Hong Kong - passed around yellow ribbons, pamphlets and even t-shirts, as police officers stood by and watched.

Organiser Hong Kong Overseas Alliance, has put the number of those who attended at 4,000 - significantly larger than the few hundred who turned up last Saturday at London's Hong Kong Economic and Trade Office, and on Sunday at Trafalgar Square.

Ms Wing Yi Kan, 27, a management consultant and one of the organisers of the London protest, told The Straits Times the alliance did it to show solidarity with the rest of the demonstrators who had taken to the streets in Hong Kong.

It has been working closely with alliances in other cities to mount a campaign worldwide - United for Democracy: Global Solidarity with Hong Kong - and this includes standardising the design of their posters and banners.

Besides the thousands who showed up, the London protest drew about 50 volunteers who took on roles from first-aiders to stewards.

Student demonstrators in Hong Kong have given the territory's Chief Executive, Leung Chun Ying, until Oct 2 to step down, before they start occupying government buildings.

The Hong Kong Overseas Alliance says it will monitor the events in Hong Kong before deciding if it should organise another rally.

One of the thousands who showed up on Wednesday night, post-graduate student Jasmine Law, 24, is worried that China will not budge on its controversial decision to screen candidates for Hong Kong's 2017 election.

"I just hope it can all be resolved peacefully," she said.