Four trustees of the 612 Humanitarian Relief Fund in Hong Kong, including singer Denise Ho Wan-see, accused of supporting rioters in violent acts in the social unrest in 2019, were reportedly arrested on Wednesday under suspicion of violating the national security law for Hong Kong.

The other three trustees of the fund under arrest are former scholar Hui Po-keung, former lawmaker Margaret Ng Ngoi-yee and former bishop Cardinal Joseph Zen Ze-kiun, according to Hong Kong online news outlet ON.cc.

Hui was reportedly arrested at the Hong Kong International Airport on Tuesday night while trying to leave the city.

Media said the four suspects were arrested for "collusion with foreign forces," an offense under the national security law for Hong Kong.

A fifth trustee of the fund, Cyd Ho Sau-lan, a former member of the Legislative Council of Hong Kong who was already imprisoned for participating in illegal gatherings, will be arrested again on Thursday for her links with the case of the relief fund, local media reported.

The arrest of the four suspects soon caught the attention of the public on China's Twitter-like Sina Weibo and topped the trending list on the platform with more than 160 million views as of Wednesday night.

Chinese netizens called for a deep investigation into these suspects and a severe punishment on them to strictly implement the national security law for Hong Kong, which aims to safeguard the national security of China and social stability of Hong Kong.

The national security law for Hong Kong is not retroactive and the current arrest means that these people still engaged in behaviors damaging the national security after the law took effect. If so, they deserve punishment, some netizens noted.

Founded on June 15, 2019, the 612 Humanitarian Relief Fund claimed to offer support and financial aid to those who were injured or arrested during the social unrest in Hong Kong that year.

However, the fund had been repeatedly exposed for unclear financing and questioned over whether its UK division served as a hub for colluding with foreign forces and meddling in Hong Kong affairs.

The National Security Department of the Hong Kong Police Force launched an investigation against the 612 Humanitarian Relief Fund for suspected contravention of the national security law for Hong Kong and other Hong Kong laws in September 2021.

The fund ceased operations in October 2021, according to Hong Kong media.

Ho and Ng were among the six suspects linked to Stand News who were arrested in December 2021 and charged with printing and disseminating inflammatory publications. However, they were released on bail after 36 hours under detention.

In April, national security department of the Hong Kong Police Force arrested Allan Au Ka-lun, a media veteran and former host of a program aired by public broadcasting service Radio Television Hong Kong, for colluding and disseminating inflammatory publications, local media said. According to the reports, the case is related to Stand News.