China’s Foreign Minister Wang Yi has issued a stern warning against any “illegal” protests in Hong Kong.
Visiting Washington, Mr Wang also warned that the matter was an “internal affair” for China.
His US counterpart, John Kerry, urged Hong Kong to exercise restraint in dealing with the protests.
Earlier, student demonstrators angry at China’s vetting of candidates for 2017 elections vowed to step up protests if Chief Executive CY Leung did not quit.
They said that protesters would start occupying government buildings if Mr Leung did not resign by Thursday.
Overnight, protesters massed outside Mr Leung’s office in a stand-off with some 200 police.
Mr Wang, the most senior Chinese official to speak openly on the matter, said: “Hong Kong affairs are China’s internal affairs. All countries should respect China’s sovereignty. For any country, for any society, no-one will allow those illegal acts that violate public order.”
However, he added: “We believe that the Hong Kong Special Administrative Region’s government has the capability to properly handle the current situation in accordance with the law.”
Mr Kerry said the US supported universal suffrage in Hong Kong, adding: “We have high hopes that the Hong Kong authorities will exercise restraint and respect for the protesters’ right to express their views peacefully.”
In China, an editorial in People’s Daily warned of “unimaginable consequences” if the protests continued, while state TV said Hong Kong’s police should be supported in their attempts to “restore the social order as soon as possible”.
Analysis: BBC’s Fergal Keane, Hong Kong
This crisis is about the most fundamental promise of democracy: who should choose the man or woman who governs Hong Kong?
The nub of the argument is with Article 45 of the Basic Law – the agreement that underpinned Hong Kong’s transition from British to Chinese rule.
It says the “ultimate aim” should be to elect the chief executive by universal suffrage. To that end, the law stipulated that a “broadly representative” nominating committee should select candidates for election.
But in August, the Standing Committee of the National People’s Congress, China’s rubber stamp parliament, ruled that candidates needed to get more than half the votes of that committee. Pro-democracy activists sensed a stitch-up: they believe the committee will be loaded with Beijing’s supporters and will ensure China controls nominations.
This is not a campaign to change China or overthrow the Communist Party, but a passionately local campaign for a big principle.
Overnight, Agence France-Presse reported that some 3,000 protesters had gathered outside Mr Leung’s offices, quoting one demonstrator, Thomas Choi, as saying: “We’re trying to surround the entire government complex and wait for CY to come back to work on Friday. We want to talk to him face to face.”
Earlier, Lester Shum, the vice-secretary of the Hong Kong Federation of Students, said: “We hope that by today or tomorrow [Thursday], Leung Chun-ying will… resign.
“Otherwise, we will announce an escalation of our movement, including occupying or surrounding different government buildings.”
Chan Kin-man, of the pro-democracy Occupy Central movement, which is also taking part in the protests, urged the students to be peaceful.
But he also called on Mr Leung to quit, saying: “We can talk to anyone in the government except him… resign for the sake of Hong Kong.”
Thousands of demonstrators remain camped out at the main protest sites in the Central business district, Causeway Bay and Mong Kok, while a fourth site opened on Wednesday on Canton Road in Tsim Sha Tsui, a major shopping district several roads south of Mong Kok.
‘A week or a month’
The Wall St Journal quoted a Hong Kong source as saying that Mr Leung was planning to ride out the protests and had been ordered by Beijing not to use violence.
A Hong Kong government source told Reuters: “It may take a week or a month, we don’t know. Unless there’s some chaotic situation, we won’t send in riot police… we hope this doesn’t happen.”
Speaking to the BBC, former Hong Kong Governor Chris Patten said he did not think China would authorise the use of force.
He said: “I cannot believe it would be so stupid as to do anything like sending in the army.”
The protesters’ numbers rose after police fired tear gas and pepper spray at the crowds on Sunday.
Lord Patten accused China of breaching commitments it made to Hong Kong before taking over sovereignty from the UK in 1997.
Hong Kong is governed under “one country, two systems”, which gives it some autonomy and freedoms not enjoyed on the mainland. The key to the protests is the interpretation of Hong Kong’s goal of “universal suffrage” for the 2017 leadership election.
Beijing ruled last month that although it would allow Hong Kong people to elect their next leader, the choice of candidates would be restricted to those approved by a pro-Beijing committee.
Hong Kong democracy timeline
- 1997: Hong Kong, a former British colony, is handed back to China under an 1984 agreement giving it “a high degree of autonomy, except in foreign and defence affairs” for 50 years
- 2004: China rules that its approval must be sought for changes to Hong Kong’s election laws
- June-July 2014: Pro-democracy activists hold an unofficial referendum on political reform and a large rally, which is followed by protests by pro-Beijing activists
- 31 August 2014: China says it will allow direct elections in 2017, but voters will only be able to choose from a list of pre-approved candidates; activists stage protests
- 22 September 2014: Student groups launch a week-long boycott of classes in protest
- 2017: Direct elections for chief executive due to take place
- 2047: Expiry of current agreements