China has the option of taking all measures necessary to prevent interference by outside forces on the issue of Taiwan, according to the president.
Beijing considers part of its territory the self-governed island, which it wants reunification with.
He spoke at the opening ceremony of the Communist Party of China's 20th National Congress.
The president said in Chinese that they would strive for peaceful reunification. We won't promise to stop using force. We can take all the measures necessary.
He said that the Taiwan question is a matter for the Chinese to resolve and that this was directed solely at interference by outside forces.
The tension around Taiwan increased this summer after Nancy Pelosi visited the island.
Despite warnings from China, the island went ahead with the visit. Beijing is recognized as the sole legal government of China by the U.S.
At the party's 19th National Congress five years ago, the issue of Taiwan was not as important as it is today.
The leaders of the party will be decided at a high-level meeting.
The names of the new core team will be revealed next weekend. An annual meeting of the Chinese government in March confirms the titles of president and premier.