China's top official in charge of relations with self-ruled Taiwan warned on Thursday of "complex changes" ahead in ties with the island, which is likely to return the independence-leaning opposition to power in mid-January polls.
Defeated Nationalist forces fled to Taiwan after losing the Chinese civil war with the Communists in 1949. Beijing has never renounced the use of force to bring what it deems a renegade province under its control.
Taiwan's independence-leaning opposition Democratic Progressive Party is expected to win January's presidential election. China says it will never countenance an independent Taiwan.
Zhang Zhijun, head of China's Taiwan Affairs Office, said in his new year greeting to Taiwan's people that 2016 will be marked by "complex changes across the Taiwan Strait and new challenges in cross-Strait ties".
"I sincerely hope relations across the Taiwan Strait continue to maintain their trend of peaceful development and that the results of this won't slip away now they have been achieved," Zhang said in a statement on the office's website.
People on both sides of the Taiwan Strait must be on high alert to "oppose any pro-independence separatist attempts to split Taiwan from China and to sabotage peace and stability", he added.
"When it comes to the important issue of safeguarding the country's sovereignty and territorial integrity, our will is unswerving and firm as a rock," Zhang said.
Relations have improved rapidly since the Nationalist's Ma Ying-jeou became Taiwan president in 2008, and the two sides have signed a series of landmark trade and tourism deals.
Ma and Chinese President Xi Jinping held a landmark meeting in Singapore in November.
Even without the prospect of an opposition election win, deep suspicions remain. China reacted angrily earlier this month at the latest U.S. plans to sell Taiwan weapons.
"Let's not wait until the road light has been extinguished before we feel its brightness, and let's not wait until the fruits of peace and development have been lost before we realize their value," Zhang said.