Activists say China is tightening its grip on the semi-autonomous city.
An exhibit in Hong Kong by Chinese-Australian artist Badiucao has been cancelled after "threats" from Chinese authorities, organisers say.
In a statement released Friday, organisers of Badiucao's show Gongle said the move had been made due to "safety concerns".
Badiucao, whose real name and identity are not known, has carved a reputation for his images satirising political suppression by Chinese authorities.
Some of his work features Winnie the Pooh in a reference to blocked memes comparing the cartoon bear to President Xi.
The artist, who was born in Shanghai and is now an Australia citizen, was due to open his first solo international exhibition in Hong Kong on Saturday.
The show was billed as a "black comedy for Hong Kong, China and the world".
The artist's work highlights themes including rights violations and abuse of power under Chinese Communist Party rule and he often satirises President Xi Jinping.
"The decision follows threats made by the Chinese authorities relating to the artist," said a statement on the news website Hong Kong Free Press, one of the event organisers.
"Whilst the organisers value freedom of expression, the safety of our partners remains a major concern."
"We regret having to make this decision, and hope there will be a chance for public to see Badiucao's work in future."
The statement did not specify the threats.
Badiucao was due to participate in a question and answer session at the opening alongside Hong Kong's young democracy leader Joshua Wong and members of the Russian anti-Kremlin Pussy Riot punk band.
The talk went ahead without the controversial artist.
Mr Wong said he was "outraged" at the decision and called on members of civil society around the world to share their experiences in order to gain "more bargaining power" in pushing for human rights and freedoms.
While Pussy Riot member Olga Kuracheva said, "we are very sorry to know that things are getting worse here".
"I would advise people not to be afraid, because one voice is not so much ... but voices of solidarity should sound loud," Ms Kuracheva said.
Amnesty International, one of the co-organisers of the exhibition, also expressed concern.
"The threat Badiucao faces exemplifies how much overseas Chinese dissidents need to consider when they do their work," said Amnesty China researcher Patrick Poon.
"It's particularly worrying that it happens here in Hong Kong as the space for freedom of expression is eroding further this year," Mr Poon added.
It is the latest blow to freedom of expression in Hong Kong as China tightens its grip on the semi-autonomous city.
Last month, Hong Kong authorities refused to renew a work visa for the Asia news editor of the Financial Times, soon after he hosted a talk by an independence activist at the city's Foreign Correspondents' Club
Hong Kong has rights unseen on the mainland, protected by an agreement made before the city was handed back to China by Britain in 1997, but there are serious concerns those freedoms are under threat.
Additional reporting: Reuters, AFP