Hong Kong democracy activist Joshua Wong was among three pro-democracy figures arrested on Thursday and Friday, ahead of another weekend of planned protests in the Chinese-ruled region which is grappling with its biggest political crisis since its handover to Beijing more than two decades ago.

Wong was "suddenly pushed into a private car on the street," on Friday, according to the official Twitter account of his political party, Demosisto, which advocates for greater democracy in Hong Kong.

The party said Wong had been taken to the police headquarters in Wan Chai — a busy commercial area — and that its lawyers were working on the case.

Wong, the face of Hong Kong's push for full democracy during protests in 2014 that paralyzed parts of the city for 79 days, was released from jail in June after serving a five-week term for contempt of court.

Wong's last tweet reiterated the protesters' five demands.

Being Born in uncertain times carries-certain responsibilities. Five Demands, Not One Less. <a href="https://t.co/09gJlPn8WL">https://t.co/09gJlPn8WL</a><br><br>HONG KONG DEMOCRATIC MOVEMENT 2019 —@joshuawongcf

Demosisto later reported that another member of the group, Agnes Chow, was also detained on Friday.

SITUATION UPDATE: Our member <a href="https://twitter.com/chowtingagnes?ref_src=twsrc%5Etfw">@chowtingagnes</a> has also been arrested this morning. She is being sent to the Wan Chai police headquarters, where <a href="https://twitter.com/joshuawongcf?ref_src=twsrc%5Etfw">@joshuawongcf</a> is currently detained. —@demosisto

The Hong Kong Free Press reported that Andy Chan, the leader of the banned pro-independence Hong Kong National Party, had been detained at the airport on Thursday while trying to board a flight to Japan.

The newspaper cited a police spokesperson who said Chan was arrested on suspicion of rioting and assaulting a police officer.

Hong Kong police later said Wong and Chow were were arrested for role in a June 21 police station protest. Both face potential charges of participating in the demonstration and inciting others to join it. Wong also is being investigated on suspicion of organizing it.

Police also confirmed the arrest of Demosisto member, Agnes Chow. (Issei Kato/Reuters)

Police have refused permission for a pro-democracy march on Saturday and an appeal by organizers to allow the demonstration to proceed was turned down on Friday.

The Civil Human Rights Front, the organizer of previous mass protests, said it would comply with the order and cancel the march from Hong Kong's central business district to Beijing's main representative Liaison Office in the city.

Unrest in Hong Kong escalated in mid-June over a now-suspended extradition bill that would have allowed people to be sent to mainland China for trial in Communist Party-controlled courts.

It has since evolved into calls for greater democracy under the "one country, two systems" formula, which guarantees freedoms not enjoyed on the mainland, including an independent judiciary.

On Thursday, China brought fresh troops into Hong Kong in what it described as a routine rotation of the garrison.

Andy Chan, founder of the Hong Kong National Party, seen here in August 2018, was reportedly detained at the airport Thursday while trying to board a flight to Japan. (Paul Yeung/Reuters)

Chinese state media stressed the troop movement was routine and Asian and Western diplomats watching the People's Liberation Army forces in the former British colony had been expecting it.

Chinese soldiers stationed in Hong Kong are not there merely for symbolic purposes and they will have "no reason to sit on their hands" if the situation there worsens, an editorial in the China Daily newspaper said on Friday.

Police have refused permission for a pro-democracy march on Saturday, but organizers have appealed against the decision.

The protest would mark five years since Beijing ruled out universal suffrage for Hong Kong and comes as Hong Kong faces its first recession in a decade, with all its pillars of growth under stress.