Tens of thousands of pro-democracy protesters have turned parts of Hong Kong into a massive street party on Monday night, with the mood turning festive just a day after riot police had deployed tear gas.

The huge crowds defied government calls to go home after Sunday's chaotic scenes, bringing key districts of the Asian financial hub to a standstill, as they vowed to stay put until the Chinese government grants them free elections.

Sunday's violence saw riot police fire clouds of tear gas as they struggled to control the protesters, in one of the biggest challenges to Beijing's rule of the semi-autonomous city.

The anger gave way to a lighter atmosphere on Monday night as riot police retreated, leaving huge masses of protesters in control of at least four major thoroughfares around the city.

Although there were few police on the scene, some protesters feared a repeat of Sunday's clashes, donning goggles and masks to protect themselves against tear gas.

The demonstrators are furious over last month's announcement by Beijing that while it will allow the city's next leader to be elected in 2017, it will insist on picking the candidates, with critics branding the move a "fake democracy".

Public anger over rampant inequality is also at its highest in years in a city once renowned for its stability.

'Umbrella revolution'

Cantonese pop music filled the air during the second day of what some are dubbing the "umbrella revolution", as protesters have been using the canopies as shields against tear gas and the scorching sun alike.

China vows not to tolerate dissent, blocks Instagram

One British sympathiser won huge cheers as he set up a barbecue and began handing out hamburgers and sausages to the protesters.

"I saw everybody was just standing around and just eating bread and bananas and I thought, 'These guys have been here for 24 hours now, and everybody needs cooked food'," Daniel Shepherd, a finance broker by day, told AFP news agency.

"Firing tear gas at students that are unarmed, I think, seems a bit excessive," added the 32-year-old.

The crowds hoisted up a makeshift copy of the "goddess of democracy" statue that graced the 1989 protests in Beijing's Tiananmen Square, while lamp posts were adorned with yellow ribbons - which, like the umbrella, have become a symbol of the movement.

But many people in Hong Kong have expressed frustration at the huge disruption the protests have caused, with the crowds blocking key junctions in the busy Causeway Bay and Mongkok shopping districts as well as the biggest protest site in Admiralty.

There was chaos on the transport network, shuttering many businesses, with schools in two central districts set to close for a second day on Tuesday.

Some social workers and teachers also went on strike after the Hong Kong Confederation of Trade Unions (HKCTU) and the Professional Teachers' Union (PTU) called for members to take action, the South China Morning Post reported.

Political headache for China

Analysts said the protests put the Chinese government in an extremely difficult position.

Communist authorities are worried that dealing with the protests too softly could encourage wider protests for greater freedoms on the mainland.

But a heavy-handed response could spark an international outcry.

"It has the potential to be such a major crisis," said Christopher Hughes, a China expert at the London School of Economics.

He warned that Hong Kong could see a repeat of China's violent crackdown on the Tiananmen Square protests.

"If they did decide to send in the tanks, who could stop them?" he asked.

"They did it in 1989 and got away with it and they're a lot more powerful now. There would be some negative impact, some business confidence, but how long will that last?"

The United States urged Hong Kong's leaders to "exercise restraint". Former colonial power Britain also expressed concern, calling for "constructive" talks to end the standoff.

Beijing moved swiftly to wipe mentions of the protests from Chinese social media - blocking photo-sharing service Instagram altogether - and reiterated its hardline stance, opposing the demonstrators' "illegal" actions.

Al Jazeera's Adrian Brown, reporting from Beijing, confirmed the outage saying "many photos from the protests were being posted on the app, and it seems that China wants to starve this story of oxygen".

He added that other blogs that mention the words "occupy" and "central" were also having problems.