The arrest of 15 of Hong Kong's most high profile pro-democracy activists has been condemned by the UK and US. 

Martin Lee, founder of the Democratic party, media tycoon Jimmy Lai and barrister Margaret Ng were among those arrested on charges of illegal assembly. 

The last British governor of Hong Kong, Lord Patten, accused China of exploiting the coronavirus pandemic to tighten its grip on the special administrative region. 

"With the world's attention focused on the appalling covid-19 epidemic, Beijing and its subservient government in Hong Kong have taken yet another step towards burying one-country, two-systems," he said.

"The arrest of some of the most distinguished leaders over decades of the campaign for democracy and the rule of law in Hong Kong is an unprecedented assault on the values which have underpinned Hong Kong's way of life for years." 

He said that the singling out of the activists did not reflect the rule of law.

"This is what authoritarian governments do. It becomes ever more clear, week by week and day by day, that Beijing is determined to throttle Hong Kong," he continued.

"The world should make clear how this further undermines any residual trust that we still have in the Chinese Communist dictatorship."

Former UK Foreign Secretary Sir Malcolm Rifkind called the arrests a "truly appalling attack" on Hong Kong's freedom and autonomy.

"The international community must speak out very clearly to show Beijing that these arrests are unacceptable and will be regarded as an assault not only on Hong Kong's freedoms but on the international rules-based order itself," he said. 

Christian crossbench peer Lord Alton has called on the UK to "urgently remonstrate" with the Chinese Government.

"These arrests are a classic example of CCP [Chinese Communist Party] opportunism - using the opportunity of the distraction of the Covid-19 pandemic as a moment to strike," he said. 

"This deadly totalitarian virus is every bit as lethal as Covid and, in combating it, the world now needs to stand in unity with Hong Kong's Democrats in defending liberal and democratic values."

Hong Kongers have become increasingly alarmed over the territory's future.  When the Hong Kong government attempted to pass an extradition bill last year that would have sent criminals to the mainland for trial, hundreds of thousands took to the streets in monthslong protests. 

Those arrested on Saturday have been charged with organising and participating in unlawful assemblies on August 18, as well as October 1 and 20 last year. 

They are due to appear in court on May 18. 

The arrests come days after Beijing officials claimed that interference in Hong Kong's affairs was not in breach of local laws. 

US Secretary of State Mike Pompeo has condemned the arrest of the pro-democracy advocates.

"Beijing and its representatives in Hong Kong continue to take actions inconsistent with commitments made under the Sino-British Joint Declaration that include transparency, the rule of law, and guarantees that Hong Kong will continue to 'enjoy a high degree of autonomy'," he said.