There is a "risk" to Taiwan's application to join the Comprehensive and Progressive Agreement for Trans-Pacific Partnership (CPTPP) if China joins first, Taiwan's government says, flagging a potential political roadblock.

The remarks come as Taiwan formally applied to join on Wednesday, less than a week after China, the world's second-largest economy.

Taiwan has been excluded from many international bodies because of China's insistence that it is part of "one-China", rather than a separate country.

Taiwan's chief trade negotiator John Deng said China always tries to obstruct Taiwan's participation internationally.

"So if China joins first, Taiwan's membership case should be quite risky. This is quite obvious," he said.

Underscoring the pressure Taiwan faces from China, the island's defence ministry reported 19 Chinese air force planes flew into Taiwan's air defence zone on Thursday, including two nuclear-capable H-4 bombers.

Taiwan's air force scrambled to intercept and warn them away.

China's air force flies almost daily in Taiwan's air defence zone, angering Taipei.

China opposes any country forming ties with Taiwan

Taiwan has been keen to win greater support from other democracies, including in its trading relations.

Mr Deng pointed to Taiwan having a different "system" from China, including Taiwan's democracy, rule of law, transparent laws and respect for personal property.

However, he said, there was no direct connection between Taiwan's decision to apply and China's.

"How mainland China comments on this is a matter for them," Mr Deng said.

When asked about Taiwan's application to the trade pact, Chinese foreign ministry spokesman Zhao Lijian reiterated a long-standing position that Taiwan is part of China.

"We are firmly opposed to any country having official ties with Taiwan and to Taiwan entering into any official treaty or organisation," Mr Zhao said.

Mr Deng said that Taiwan, a major semiconductor producer, has applied to join under the name it uses in the World Trade Organization (WTO) — the Separate Customs Territory of Taiwan, Penghu, Kinmen and Matsu.

Taiwan is a member of the WTO and Asia-Pacific Economic Cooperation (APEC) grouping.

"I stress that Taiwan is a sovereign, independent nation. It has its own name. But for trade deals the name we have used for years is the least controversial," Mr Deng said.

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The CPTPP application was made to New Zealand's government, which handles the paperwork.

Mr Deng said he was not able to predict when Taiwan may be allowed to join the CPTPP, noting that Britain's application was proceeding the fastest at present.

Britain began negotiations in June.

The original 12-member agreement, known as the Trans-Pacific Partnership (TPP), was seen as an important economic counterweight to China's growing influence.

But the TPP was thrown into limbo in early 2017 when former US president Donald Trump withdrew the United States.

The grouping, which was renamed the CPTPP, links Canada, Australia, Brunei, Chile, Japan, Malaysia, Mexico, New Zealand, Peru, Singapore and Vietnam.

The CPTPP, which took effect in 2018, includes agreements on market access, movement of labour and government procurement.

ABC/Wires