China's ambassador to Britain on Monday warned against any "external interference" in Hong Kong, where months of protests have erupted into increasingly violent confrontations.
At a press conference in London, Liu Xiaoming singled out Britain and the United States for meddling in internal Chinese affairs.
"We would like to tell those external forces that the Chinese government remains steadfast... to oppose any" external interference in Hong Kong affairs, he said.
The comments came as Britain, the former colonial power in Hong Kong, expressed concerns about the escalation of violence between protesters and authorities.
Riot police on Monday sought to dislodge several hundred pro-democracy protesters who occupied a university and had set fire to its main entrance.
Police, who have in recent days been attacked with arrows, used tear gas and fired live rounds.
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"The UK is seriously concerned by the escalation in violence from both the protesters and the authorities around Hong Kong university campuses," the British Foreign Office said.
"It is vital that those who are injured are able to receive appropriate medical treatment, and that safe passage is made available for all those who wish to leave the area.
"We need to see an end to the violence, and for all sides to engage in meaningful political dialogue ahead of the District Council elections on Sunday." Liu Xiaoming accused the protesters of trying to destabilise and paralyse Hong Kong to "seize power".
"Hong Kong citizens live under black terror created by violent extremism with their life and property under severe threat," he said.
He warned that Hong Kong was "sliding into the abyss" and if the violence continues, "the future will be unimaginably dreadful".
"The once Oriental star is turning into the Oriental scar," he told reporters.