Police in Hong Kong have been photographed carrying boxes marked 'corrosive' into the government's main headquarters as officers urge demonstrators to end their pro-democracy protests.

The photo, which emerged on social media, appears to show officers carrying equipment marked 'corrosive' and 'toxic' into the main government building as the protests escalate.

The photograph was uploaded to Facebook by Leung Kwok Hung, a left-wing political activist and member of the Legislative Council of Hong Kong.

Hong Kong police warned the protesters of "serious consequences" if they attempt to charge government buildings during their campaign for democracy.

The Communist Party-run newspaper People's Daily upped the warning, saying there would be "unimaginable consequences" to demonstrators unless the protests cease.

Tens of thousands of protesters have lined the streets calling for the city's leader Leung Chun-ying to step down.

The Honk Kong government has urged the protesters in the "umbrella revolution" to stand down peacefully so public services can resume in the city.

A spokesperson said: "About 3,000 government officials will try their best 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."

Tear gas has already been deployed by police in an attempt to suppress the protests.

Elsewhere, China's Foreign Minister Wang Yi warned other governments not to intervene in the protests in Hong Kong during a visit to Washington for scheduled talks with US Secretary of State John Kerry.

"Hong Kong affairs are China's internal affairs," he said.

"All countries should respect China's sovereignty and this is a basic principle of governing international relations.

"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."

hong kong mobile phones
Pro-democracy demonstrators hold up their mobile phones during a protest near the Hong Kong government headquarters Dale de la Rey/AFP