Taiwanese authorities said Monday they were probing criminal gang links to a pro-China protest which targeted Hong Kong pro-democracy activists and rebel legislators in Taiwan.

The activists were visiting to attend a forum aimed at linking democracy movements in Hong Kong and Taiwan earlier this month. They were blasted by pro-China groups on the island as promoting a joint independence movement.

Although Taiwan is self-ruling, it has never formally declared independence from Beijing, and China considers it part of its territory.

The forum was organised by Taiwan's New Power Party, which advocates for recognition of Taiwan as a nation.

The Hong Kong campaigners were greeted at Taipei airport by 200 protesters, with scuffles occurring after six broke through a police line protecting the activists.

Prosecutors told AFP Monday they were probing whether there were gang links.

Chang Wei, son of former gang leader Chang An-lo, known as "White Wolf", has been questioned over the clashes and barred from leaving Taiwan pending further investigation.

The senior Chang, who headed the Bamboo Union Gang, now leads a small pro-unification party that regularly organises rallies in support of Beijing.

Police confirmed that Chen Tzu-chun, a leader of the Four Seas Gang, is also under investigation over the protests. He remains in custody over a number of cases.

Speaking to the Liberty Times, Taiwan police chief Chen Kuo-en said two gangs had participated in the demonstrations.

"The police will not tolerate ... this kind of interference," Chen said.

The Four Seas and Bamboo Union are among Taiwan's biggest criminal gangs, known for their involvement in smuggling and gambling.

Chang An-lo has openly supported politicians from the Beijing-friendly Kuomintang party, while Four Seas members were previously accused of attacking a pro-independence politician.

Legislator Nathan Law, one of the group to visit Taiwan, was also attacked when he returned to Hong Kong as demonstrators threw liquid and tried to hit him.

Law, 23, who advocates self-determination for Hong Kong, said those attacks were also an example of "gangster politics" and accused the Chinese Communist Party of trying to suppress democratic movements.

Beijing has grown increasingly incensed over pro-independence calls from young activists in Hong Kong.

Chinese authorities have also been ratcheting up pressure on Taiwanese president Tsai Ing-wen as she refuses to acknowledge the concept there is only "one China."

Last week China's only aircraft carrier proceeded slowly through the Taiwan Strait in what was seen as a show of strength as tensions escalate.

The drills came as a heated war of words intensified between Beijing and US President-elect Donald Trump, who broke convention by speaking directly to Taiwanese president Tsai Ing-wen and even suggested Washington could jettison its decades-old "one China" policy.

Despite not having official diplomatic ties since it recognised Beijing in 1979, the US is Taiwan's most powerful ally and arms supplier.