Beijing on Thursday expressed strong dissatisfaction with criticism made by western countries about arrests made over a now-defunct fund that raised money for the legal and medical fees of protesters, as sources said a fifth person has been arrested.

Sources said Cardinal Joseph Zen, barrister Margaret Ng, singer Denise Ho and cultural studies scholar Hui Po-keung have been released on bail following their arrest by national security officers.

The fifth person believed to have been arrested is former lawmaker Cyd Ho, who is serving a prison term in connection with a banned protest.

In a statement, the Commissioner's Office of the Foreign Ministry in Hong Kong said the US State Department, US Congress, EU foreign policy chief, Canada's foreign affairs minister and some other foreign politicians had made baseless accusations against Hong Kong police who took appropriate action against people connected to the 612 Humanitarian Relief Fund.

A spokesman said police officers are upholding the rule of law, urging the foreign countries and politicians to stop interfering in Hong Kong's internal affairs.

"These people allegedly colluded with foreign forces and undermined national security," the spokesman said.

"The foreign forces know very well where these people went and what they did. Stop playing dumb!"

The US State Department said the arrests show Hong Kong authorities have again demonstrated they will pursue all means necessary to stifle dissent and undercut protected rights and freedoms.

EU foreign policy chief Josep Borrell said he was following the arrests with "great concern".

Mélanie Joly, Canada’s minister for foreign affairs, said the arrests were “deeply troubling”.

"The ongoing targeting of civil society groups erodes the rights and freedoms of Hong Kong residents guaranteed under Hong Kong’s Basic Law," she wrote on Twitter.

Meanwhile, the Catholic Diocese of Hong Kong has said it is extremely concerned about the condition and safety of Zen.

"We have always upheld the rule of law. We trust that in the future we will continue enjoying religious freedom in Hong Kong under the Basic Law," a statement said.