Pro-democracy protesters in Hong Kong clashed with police outside government offices as tensions ran high Friday morning, despite an eleventh-hour agreement for talks, as China said the demonstrators were "doomed to fail".

Although most overnight demonstrators had gone home by the morning, more than 100 remained outside the government complex which is now the focal point of protests that have brought parts of the city to a standstill for five days.

Demonstrators are sceptical over what can be gained by the discussions with the government of Chief Executive Leung Chun-ying, which were agreed late Thursday to defuse escalating tensions as crowds demanded Leung's resignation.

And on Friday China reiterated its tough stance ahead of the first popular ballot in 2017 to choose the Hong Kong leader, saying there was "no room to make concessions on important principles".

Police pushed through around 100 demonstrators who were blocking an exit Friday morning, saying that a seriously ill officer needed to be let out in an ambulance.

In chaotic scenes, protesters refused to move shouting "liar, liar," in response to the request to move, with police finally forcing their way through to make a path for the ambulance.

Relations between protesters and police have deteriorated since tear-gas was fired to disperse crowds last Sunday and boxes carrying rubber bullets were seen being carried by officers Thursday.

Students vowed to continue their occupation after Leung announced that the government was willing to hold talks with them.

Many are still demanding that the leader step down -- and are not impressed by his nomination of his deputy to represent the government in the talks.

"I think he is avoiding people who are voicing their views," Abigail Hon, 19, told AFP Friday morning.

"From now on I am going to stay overnight. We hope that Leung can face the problem and respond to what we demand right now," she said, adding that she wants Leung to speak directly with the students.

The Occupy Central group said it welcomed the talks, adding it hoped they would "provide a turning point in the current political stalemate".

It was not clear when the talks would start.

International pressure

On August 31, China said Hong Kongers would be able to vote for their next chief executive in 2017 but that only candidates vetted by a loyalist committee would be allowed to stand, a decision dismissed as "fake democracy" by campaigners.

Their protests have attracted support from people and politicians around the world.

Huge crowds have shut down central areas of the Chinese city with mass sit-ins all week. Demonstrators had set a midnight Thursday deadline for Leung to quit and for Beijing to guarantee full democracy to the former British colony.

But China has strongly backed Leung and pledged support for police over the protests, which pose a huge challenge to its rule at a time when the Communist Party is cracking down on dissent on the mainland.

In an editorial Friday the People's Daily, the Communist Party mouthpiece, repeated Beijing's unbending response.

"Upholding the (August 31) decision of the standing committee of the National People's Congress is the necessary decision, and the only decision," it said, adding that the protests are "against legal principles, and doomed to fail".

Analysts say it is unlikely Leung will step down, in what would be a massive loss of face for Beijing and the Hong Kong establishment.

"If Beijing forces him to resign, they will be seen to be buckling under pressure from the protesters," said Willy Lam, a China scholar at the Chinese University of Hong Kong.

Authorities have scrubbed mentions of the protests from Chinese social media, while rights groups say more than a dozen activists have been detained on the mainland and as many as 60 others questioned for expressing support for the Hong Kong crowds.

Beijing's latest comments came after China's foreign minister issued a stern warning to the United States not to meddle in its "internal affairs".

But international concern continues to grow, with the European Union calling on all sides to remain calm.

"In the light of the ongoing demonstrations, we welcome the restraint shown by both sides. We urge all sides to continue to exercise this restraint," an EU spokeswoman said Thursday.

Chris Patten, the last British governor of Hong Kong, welcomed the government's offer to talk with students, in comments to the BBC.

However, he called Beijing "foolish" for not trusting the people of Hong Kong to elect a suitable candidate to lead the financial hub.