Hong Kong’s pro-democracy Stand News online media outlet says it is ceasing operations following a police raid and arrests of current and former editors and board members.

The outlet issued a statement on Wednesday saying its website and social media are no longer being updated and will be taken down. It says all employees were dismissed.

Police raided the Stand News office earlier in the day after arresting six people on charges of conspiracy to publish a seditious publication. The move is the latest in an ongoing crackdown on dissent in the semi-autonomous Chinese city.

More than 200 officers were involved in the raid, police said. They had a warrant to seize relevant journalistic materials under a national security law enacted last year.

The six were arrested early on Wednesday under a colonial-era crimes ordinance for conspiracy to publish a seditious publication, and searches of their residences were underway, police said.

Those convicted could face up to two years in jail and a fine of up to 5,000 Hong Kong dollars (£480).

According to the local South China Morning Post newspaper, police arrested one current and one former editor at Stand News, as well as four former board members including singer and activist Denise Ho and former lawmaker Margaret Ng.

Police did not identify those who were arrested.

A Facebook post early on Wednesday on Ho’s account confirmed that she was being arrested. A subsequent message posted on her behalf said she was okay and urged friends and supporters not to worry about her.

That post drew nearly 40,000 likes and 2,700 comments, mostly from supporters.

Early on Wednesday, Stand News posted a video on Facebook of police officers at the home of a deputy editor, Ronson Chan, where they were investigating the alleged crime.

Chan, who is also chair of the Hong Kong Journalists Association (HKJA), was taken away for questioning, the organisation confirmed in a statement.

Chan, who was later released, told media the police seized his electronic devices, bank cards and press card.

The arrests come as authorities crack down on dissent in the semi-autonomous Chinese city. Hong Kong police had previously raided the offices of the now-defunct Apple Daily newspaper, seizing boxes of materials and hard drives to assist in their investigation and freezing millions in assets that later forced the paper to cease operations.

Police charged former Apple Daily publisher Jimmy Lai with sedition on Tuesday.

Stand News earlier this year said it would suspend subscriptions and remove most opinion pieces and columns from its website due to the national security law. Six board members had also resigned from the company.

The HKJA urged the city’s government to protect press freedom in accordance with Hong Kong’s mini-constitution, the Basic Law.

“The Hong Kong Journalists Association (HKJA) is deeply concerned that the police have repeatedly arrested senior members of the media and searched the offices of news organisations containing large quantities of journalistic materials within a year,” it said in a statement.

Benedict Rogers, co-founder and CEO of the non-governmental organisation Hong Kong Watch, said the arrests are “nothing short of an all-out assault on the freedom of the press in Hong Kong”.

“When a free press guaranteed by Hong Kong’s Basic Law is labelled seditious, it is a symbol of the speed at which this once great, open, international city has descended into little more than a police state,” he said.

Wednesday’s arrests also followed the removal of sculptures and other artwork from university campuses last week. The works supported democracy and memorialised the victims of China’s crackdown on democracy protesters at Beijing’s Tiananmen Square in 1989.