GENEVA (Reuters) – The U.N. human rights office voiced concern on Friday that “vague and overly broad” provisions in Hong Kong’s new national security law may lead to activists being prosecuted in violation of fundamental freedoms of assembly and expression. 

National security legislation imposed by China this week on Hong Kong will punish crimes of secession, subversion, terrorism and collusion with foreign forces with up to life in prison, heralding a more authoritarian era for the city. 

“We are alarmed that arrests are already being made under the law with immediate effect, when there is not full information and understanding of the scope of the offences,” U.N. human rights spokesman Rupert Colville said. 

Hundreds were arrested at a protest on Wednesday, a day after the new law went into effect, and at least 10 have been charged under it, he told a Geneva news briefing. 

“We are concerned that the definition of some of the offences contained in the law are vague and overly broad and do not adequately distinguish between violent and non-violent acts. This may lead to discriminatory or arbitrary interpretation and enforcement of the law, which could undermine human rights protection,” Colville said. 

The offence of “collusion with a foreign country or with external elements” could leave activists liable to prosecution for exercising their rights to freedom of expression, association and peaceful assembly, he said. 

The law’s provisions guaranteeing the presumption of innocence and rights to due process and fair trial must be upheld, in line with international treaties protecting civil and political rights, he said.