As crowds swelled for the sixth straight night, student leaders said they would occupy government buildings across the city if their demands were not met. Thousands were circling government headquarters by Thursday morning.

"You thought you can rule this place," said Alex Chow,  secretary-general of the Hong Kong Federation of Students,  in front of a cheering crowd late on Wednesday. "If you don't respond to the demand of the Hong Kong people, we will paralyse the government."

But the Government's plan appears to sit out the protest and wait for momentum to slow, or for the disruption of daily life to turn public opinion against the protest movement.

Mr Leung and his advisers, with support from China's leaders, do not plan to use force to disperse demonstrations, but will also not engage in negotiations with protest leaders for now. There is also no serious discussion of Mr Leung resigning, The New York Times reported, citing unnamed sources.

Reuters quoted a Government source as saying that the chief executive "appeared ready to allow the anger to subside, and would only intervene if there was looting or violence". The person added: "We have to deal with it peacefully, even if it lasts weeks or months."

But the threat of escalation has come as student leaders seek to force a result, with protest momentum peaking over a two-day public holiday in Hong Kong.

Student leaders estimated that crowds outside Government headquarters on Wednesday night were "at least over 100,000" if not in the hundreds of thousands. While police have not provided an estimate of the sustained crowds over almost a week, support organisers claim  this has been among the city's largest mass demonstrations, rivalling the 2003 protest against anti-subversion laws.

In practice, authorities have few options to confront protesters because of the huge crowd sizes. An attempt to disperse crowds by using tear-gas early in the protests, when crowds were smaller, backfired and significantly strengthened public sentiment towards the movement.

But the spontaneity of the growing crowds has added to the unpredictability of the protests. Thousands of protesters paralysed a stretch of Canton Road, an upmarket shopping strip popular with mainland Chinese tourists, in actions not sanctioned by protest leaders.

Leaders of the protests have urged demonstrators to focus on existing sites under its control, in Admiralty, Mongkok and Causeway Bay.

"We need to think about whether you can sustain new occupation sites," Occupy Central co-founder Chan Kin-man said. "We are under tremendous pressure particularly after midnight when we have to safeguard [existing occupation areas]."

Beijing has also suspended tour groups to Hong Kong, although this will not affect individual travel.

Meanwhile, Chinese Foreign Minister Wang Yi has warned Washington to back off from criticism of its handling of the protests sweeping Hong Kong, saying it would not tolerate "illegal acts".

"The Chinese government has very firmly and clearly stated its position. Hong Kong affairs are China's internal affairs," Mr Wang told his American counterpart John Kerry in the US capital ahead of their meeting on Wednesday.