Police seen carrying rubber bullets and other kit into compound housing offices of chief executive, who is facing calls to quit

Tensions rose in Hong Kong on Thursday as protesters’ deadline for the chief executive’s resignation approached and the government urged people to clear the streets.

Police warned of serious consequences if students tried to occupy official buildings, as they have threatened to do if Leung Chun-ying does not quit by midnight. Officers were seen carrying rubber bullets and other equipment into the compound housing the chief executive’s offices.

Earlier the Chinese government hardened its public remarks about the movement. The official People’s Daily newspaper, the voice of the Communist party, said China was “very satisfied” with Leung and had full confidence in his leadership – disappointing demonstrators who had hoped Beijing would jettison Leung to calm the situation.

The newspaper’s front-page commentary also supported the police handling of the “illegal activities” and accused protesters of threatening to drag the region into chaos.

Tens of thousands of people have occupied the roads in Admiralty, close to government offices. The crowd outside Leung’s offices swelled with demonstrators, some of whom donned goggles and masks for the first time in several days.

Pictures shared widely on social media showed police carrying in long boxes, a barrel labelled “Round, 38mm rubber baton multi” and another with “1.5 in, CS” on it, a possible reference to CS gas.

Police have maintained a low-key presence since the use of pepper spray and teargas against protesters on Sunday galvanised thousands more people to join the movement. The police spokesman Steve Hui said: “We stress that police will not tolerate any illegal surrounding of government buildings.”

Men with binoculars could be seen watching the crowds from the People’s Liberation Army building next door, as they have done for much of the protests.

Leaders of the groups that helped to spark the protests – the Hong Kong Federation of Students, Scholarism and Occupy Central – vowed to keep working together. “In the coming days we will team up to support the movement and provide resources. We will fight until the very end,” the student leader Joshua Wong announced to huge cheers.

Occupy Central leaders have previously said they trusted the students, while making it evident they had some concerns about plans to escalate action.

Organisers urged the elderly and those accompanied by children to stay away from government offices. They took no questions from media.

The Hong Kong government said in a statement: “About 3,000 government officials will try their best tomorrow to return to work as [much] as possible. To maintain public service, the government headquarters must operate as usual. We urge the Occupy Central leaders and organisers to stop the movement immediately.”

Some have dubbed the movement the “umbrella revolution”, but participants have been at pains to stress they do not seek independence from China nor the overthrow of the Communist party. Rather they are demanding the right to a real choice of the next chief executive. As the protests gained pace, they also demanded the resignation of the incumbent.

China has promised Hong Kong universal suffrage for the 2017 election, reflecting the greater freedoms the region enjoys under the “one country, two systems” framework.

Hong Kong residents knew that limits would be imposed on their choice, but many were angered by the strictness of the restrictions announced, which effectively ruled out any prospect of a democrat standing. Only two or three candidates will be permitted, and they will have to win the backing of a committee of Beijing loyalists.

China’s foreign minister, Wang Yi, warned foreign governments not to intervene as he visited Washington for scheduled talks with the US secretary of state, John Kerry.

“Hong Kong affairs are China’s internal affairs … All countries should respect China’s sovereignty and this is a basic principle of governing international relations,” Wang said. “I believe for any country, for any society, no one would allow those illegal acts that violate public order. That’s the situation in the United States and that’s the same situation in Hong Kong.”

Speaking alongside Wang at a press briefing, Kerry told reporters: “As China knows, we support universal suffrage in Hong Kong, accordant with the Basic Law [Hong Kong’s mini-constitution]. We believe an open society with the highest possible degree of autonomy and governed by rule of law is essential for Hong Kong’s stability and prosperity … And we have high hopes that the Hong Kong authorities will exercise restraint and respect the protesters’ right to express their views peacefully.”

Unusually, US officials said the two men would meet for a second time later in the day, at the Chinese delegation’s request. The state department spokeswoman Jen Psaki told reporters: “It’s clear that we want the people of Hong Kong to have a broad choice of candidates.”

Supporters of the Hong Kong demonstrators protested outside the Chinese embassy in London on Wednesday night, and gathered at sites across the US.

Mainland authorities have been working overtime to control references to the protests tightly, and the South China Morning Post reported that they had suspended visits by tour groups to Hong Kong.

The China National Tourism Administration told operators not to organise group visits to the city, though people who had booked before Wednesday were not affected. Mainland tourists account for around 75% of visitors to Hong Kong, but most come as individuals.