It is up to the Chinese people to resolve the Taiwan issue and China will never renounce the right to use force but will strive for a peaceful resolution, President Xi Jinping said on Sunday at the opening of a major party meeting.

Taiwan, which China views as its own territory, responded that it will not back down on its sovereignty or compromise on freedom and democracy.

Tensions between the Beijing and Taipei rose dramatically in August after China staged war games near Taiwan following the visit to Taiwan of U.S. House Speaker Nancy Pelosi. Those military activities have continued though at a reduced pace.

In a speech opening the ruling Communist Party's 20th party congress in Beijing, Xi said China always "respected, cared for and benefited" Taiwan's people and was committed to promoting economic and cultural exchanges across the Taiwan Strait.

"Resolving the Taiwan issue is the Chinese people's own business, and it up to the Chinese people to decide," he said.

"We insist on striving for the prospect of peaceful reunification with the greatest sincerity and best efforts, but we will never promise to give up the use of force and reserve the option to take all necessary measures."

That option is aimed at "interference" by external forces and a "very small number" of Taiwan independence supporters rather than the vast majority of the Taiwanese people, Xi said.

"The historical wheels of national reunification and national rejuvenation are rolling forward, and the complete reunification of the motherland must be achieved, and it must be achieved!" he added, to a long round of applause.

Taiwan's presidential office said in response that the Republic of China – the island's official name – was a sovereign and independent country.

"Taiwan's position is firm: no backing down on national sovereignty, no compromise on democracy and freedom, and meeting on the battlefield is absolutely not an option for the two sides of the Taiwan Strait," it said in a statement.

"This is the consensus of Taiwan's people," the presidential office said, adding the national security team was keeping a close eye on developments at the congress.

In her national day speech on Monday, Taiwan President Tsai Ing-wen said war between Taiwan and China was not an option and reiterated her willingness to talk to Beijing, even as she pledged to keep boosting Taiwan's defenses.

Speaking to reporters on Sunday, Taiwan Premier Su Tseng-chang – who China put sanctions on last year, saying he was a separatist – said Xi should focus on his own people.

Referring to rare banners of political protest on an overpass in Beijing on Thursday, Su said, "Xi Jinping should pay attention to the smoke and protest banners on the Sitong Bridge in Beijing, rather than always thinking about using force to deal with Taiwan."

China refuses to speak to Tsai, considering her a separatist.

Beijing has offered Taiwan a "one country, two systems" model of autonomy, the same formula it uses for Hong Kong. But all mainstream Taiwanese political parties have rejected that proposal and it has almost no public support, according to opinion polls.

Taiwan says only its people can decide their own future and that Beijing's claims are void as the People's Republic of China has never governed any part of the island.