Hong Kong democracy activists have launched a new push to continue their fight among residents living abroad in the wake of a sweeping crackdown by Beijing and changes to the the semi-autonomous Chinese city's electoral system aimed at shutting out opposition voices.

In a letter titled the “2021 Hong Kong Charter," the activists stated that, “Numerous Hongkongers have no choice but to leave in exile, while those remaining in their city are living with the constant fear of being politically persecuted on any day."

“The 2021 electoral reform imposed by the Chinese Communist Party further annihilated the democratic elements in our elections, putting the last nail in the coffin for “One Country, Two Systems,” the letter said, citing the framework for running the city after its handover from British colonial rule in 1997.

The letter, cosigned by eight prominent opposition figures, calls for international support to counter what they called the “global aggression” of China's ruling Communist Party, along with reforms to the government and police force and the abolishment of a sweeping national security law imposed last year. Dozens of activists including former lawmakers have been charged under the law, prompting many to seek asylum abroad.

“Under such high pressure from China, the diaspora from Hong Kong have more responsibility than ever to speak out and ensure we continue to draw international concern,” Nathan Law who now resides in the U.K., said during an online news conference Sunday. “We hope our overseas communities can continue to fight until the day we can elect our own leaders.”

Hong Kong was rocked by months of antigovernment protests in 2019 that were met with increasingly repressive measures by security forces and the authorities in Beijing.

China's legislature this month approved changes to election rules in the city that will virtually eliminate the influence of any political opposition, bringing strong criticism from the U.S. and the U.K., which ruled Hong Kong as a colony for 156 years. The changes tighten Beijing's control over the selection of Hong Kong's leader, along with the makeup of its legislative council.

China had pledged to allow the city to retain freedoms not permitted elsewhere in the country for 50 years, but its recent steps are seen as a betrayal.

British Foreign Secretary Dominic Raab on Saturday said Beijing’s decision to “impose radical changes to restrict participation in Hong Kong’s electoral system ... is part of a pattern designed to harass and stifle all voices critical of China’s policies.”

Raab said the moves amount to the third breach of a 1984 agreement between the sides that Britain hoped would protect Hong Kong's freedoms after the handover of power.