The clock is counting down on Hong Kong protesters' ultimatum for the territory's leader to quit or face the occupation of government buildings.

CY Leung has been given until the end of Thursday (local time) to step down or face a significant escalation in the standoff.

Around 200 people gathered outside his office in the early hours as 50 police officers stood guard from behind metal barriers.

An occupation of buildings would mark a new stage in the peaceful demonstrations, raising fears police could again use tear gas to keep control.

China appears to be slowly losing patience with the protesters' refusal to move from the streets since late last week.

Communist Party-run newspaper People's Daily has warned of "unimaginable consequences" if activists ignore calls to go home.

State TV, meanwhile, has urged protesters to support efforts to "deploy police enforcement decisively" and "restore the social order in Hong Kong as soon as possible".

The demonstrators involved in the so-called "umbrella revolution" are railing against an order which means they will have to choose their leader, or chief executive, from among Communist loyalists chosen by Beijing.

Mr Leung has reportedly said he is willing to let the protests continue for weeks if necessary - but has refused to resign.

He was booed and heckled by hundreds of people on Wednesday as he arrived for a flag-raising event to mark China's National Day. People turned their back as the ceremony began.

Protester numbers swelled to the tens of thousands on the public holiday as many more people joined the student-dominated crowds.

A network of food and drink supply stations has formed as the demonstrators seemingly dig-in for the long haul.

Many are equipped with goggles, umbrellas and plastic macs in case police again resort to tear gas and baton charges, as they did at the weekend.

US Secretary of State John Kerry said he had "high hopes" authorities would use restraint.

China has issued a stern warning to other countries not to meddle in its affairs.

"The Chinese government has very firmly and clearly stated its position. Hong Kong affairs are China's internal affairs," foreign minister Wang Yi told Mr Kerry ahead of talks.

Protesters also forced roads to be closed outside the Chinese embassy in London on Wednesday as a large crowd gathered peacefully to express their solidarity.

Around 5,000 people also massed in Taipei, the capital of Taiwan, a renegade province in the eyes of China's government