China will never allow anyone to "make a great fuss" about its territorial sovereignty and maritime rights, President Xi Jinping said in his New Year's address, while China's top official in charge of Taiwan ties warned of risk ahead in 2017.

China's increasingly assertive moves to push its territorial claims in the disputed South China Sea, including building artificial islands, has unnerved its neighbours.

"We adhere to peaceful development, and resolutely safeguard our territorial sovereignty and maritime rights and interests," Xi said, in comments carried by state media late on Saturday.

"Chinese people will never allow anyone to get away with making a great fuss about it," he said, without elaborating.

China claims most of the South China Sea. Neighbours Brunei, Malaysia, the Philippines, Taiwan and Vietnam also have claims.

While Xi made no direct mention of self-ruled Taiwan, aside from extending New Year's greetings to them, the head of China's policy-making Taiwan Affairs Office in his New Year's message said that 2017 would see uncertainty.

"Looking ahead to 2017, the situation in the Taiwan Strait is complex and serious, and the development of relations are facing many uncertain factors and risk," Zhang Zhijun said, according to the official Xinhua news agency.

China hopes that people on both sides can show resolve and courage, to ensure the "correct direction" of the peaceful development of ties and work to maintain peace and stability across the Taiwan Strait, he added.

Taiwan President Tsai Ing-wen said on Saturday that Taiwan will be "calm" when dealing with China, but uncertainties in 2017 will test the island and its national security team, even as she recommitted to maintaining peace.

China is deeply suspicious of Tsai, who it thinks wants to push for the formal independence of Taiwan, a self-governing island that Beijing regards as a renegade province.

U.S. President-elect Donald Trump angered China last month when he spoke to Tsai in a break with decades of precedent and cast doubt on his incoming administration's commitment to Beijing's "one China" policy.

China's military has become alarmed by what it sees as Trump's support of Taiwan and is considering strong measures to prevent the island from moving toward independence, sources with ties to senior military officers said.