Taiwan lashed out at Hong Kong Monday, saying the city had recently denied visas to several Beijing-sceptic Taiwanese politicians as the island's relations with China worsen.

Ties between Taiwan and Beijing have turned increasingly frosty since new president Tsai Ing-wen and her Democratic Progressive Party (DPP) took office in May.

Although Taiwan is self-ruling it has never declared formal independence and China still sees it as part of its territory.

Beijing is highly suspicious of Tsai and the DPP, which is traditionally an independence-leaning party.

Now Taiwan is accusing semi-autonomous Hong Kong of doing Beijing's bidding by refusing to allow a series of DPP politicians to enter the city.

Two DPP lawmakers say they were denied visas to attend forums. A third was refused entry when his connecting flight was cancelled in the southern Chinese city in August.

A professor with DPP connections was also refused a visa last month and leading protesters from Taiwan's anti-China "Sunflower Movement" say they have been denied visas in the past.

Taiwan's China affairs minister Chang Hsiao-yueh described the denials as "very unreasonable".

"Hong Kong should not have been pressured by China to restrict our lawmakers travelling to Hong Kong," she told reporters.

"We express utmost dissatisfaction and regret to the Hong Kong government."

Chang told parliament later Monday that Taiwan's office in Hong Kong had approached local government officials over the issue but had yet to receive "good results", without elaborating.

Taiwanese media quoted a Hong Kong forum organiser as saying China's Taiwan Affairs Office had instructed that "all DPP officials" be denied entry to Hong Kong.

An immigration spokeswoman in Hong Kong said the department did not comment on individual cases.

Taiwanese residents can usually apply online for "pre-arrival registration" for Hong Kong free of charge.

Beijing is pressuring Tsai to accept the concept that there is only "one China", as did her predecessor Ma Ying-jeou from the China-friendly Kuomintang party. She has refused to do so.

As a result, Beijing has cut all official communications with her government. It has been accused by Taipei of pressuring a number of countries to deport Taiwanese fraud suspects to China rather than their home territory.

Taiwan has also blamed China for blocking it from attending a major United Nations aviation meeting in Canada starting this week.