Pro-democracy activists have called on European leaders to speak out against the imposition of national security legislation in Hong Kong, and to put pressure on Beijing to abandon the move.

Demosisto leader Joshua Wong, former Demosisto lawmaker Nathan Law, and Sunny Cheung from Network DIPLO made the appeal outside the Central Government Offices on Wednesday.

They said they have launched a petition urging European leaders to oppose the national security legislation and that so far they have obtained 70,000 signatures.

They warned that European Union countries would be affected by the law, as the bloc is China's most significant trading partner, with substantial investments in Hong Kong.

Wong said that although the EU and seven individual European countries have expressed opposition or concerns about the incoming law, at least 15 European countries – including Denmark, Greece, Ireland, Italy, and Spain – are yet to publish an official position.

Law said world leaders should stand up to Beijing's authoritarianism and expansionism as it is "a global effort".

"Hong Kong is definitely at the frontline, because we can see that China has been threatening its periphery areas for decades," Law said, citing Xinjiang and territorial disputes over the South China Sea.

"We think that the European Union, which is united with the idea of democracy and freedom should be more vocal on the expansionist communist party in China in order to combat this revival of authoritarianism," Law said.

"In this critical time, we would like to remind these democratic institutions and countries that we need to join hands to fight against the revival of authoritarianism."

Meanwhile, a group whose Chinese name translates as "Anti-black money, anti-Hong Kong independence concern group" staged a protest on Wednesday afternoon outside the US Consulate, accusing Washington of interfering in China's internal affairs.

In a letter handed over to a consulate security guard, the group said violent protests have made a national security law a necessity, in order to protect people's safety and the city's prosperity.

They also accused the US of double standards, contrasting how politicians' responded to the protests in Hong Kong and the police's use of force with how the Trump administration is responding to current protests in America.