"If the situation deteriorates further into unrest, uncontrollable by the Hong Kong Special Administrative Region (SAR) government, then the central government will not sit by and watch," Liu said during a press conference in London.
The central government fully "understands, respects and supports" the SAR government led by Chief Executive Carrie Lam, and Beijing believes Lam's government and police are capable of handling the situation and restore order, Liu stressed.
This violent behavior shows early signs of terrorism, Liu noted, adding that offenders involved in these violent acts must be brought to justice.
On Wednesday, Trump tied the ongoing China-U.S. trade talks to a resolution for Hong Kong. He tweeted: "Of course, China wants to make a deal. Let them work humanely with Hong Kong first! I have ZERO doubt that if President Xi wants to quickly and humanely solve the Hong Kong problem, he can do it. Personal meeting?"
He warned of foreign forces behind the violence in the city. Some foreign organizations have been financially supporting protests, and some foreign officials have been seen meeting radical protesters, and they want to use Hong Kong to prevent China from developing smoothly, the ambassador said.
On the question of the impact of the situation in Hong Kong on China-UK ties, the ambassador said that some politicians in Britain can't get over the colonial hangover, and they still see Hong Kong as a British colony.
The UK has no jurisdiction and power over Hong Kong and the 1984 joint declaration was made to ensure the handover of Hong Kong and a smooth transition later, he said.
The bilateral ties are based on mutual respect on sovereignty and internal affairs, and as long as the UK government follows this principle, the relationship would move along the Golden Era, he said.