In a strong caution to advocates of Taiwanese independence, he said China was "firmly against" critics of Beijing's policy, claiming that "no one and no party can change the fact that Taiwan is part of China".
Up until 1979, China had conducted routine artillery bombardment of Taiwan-controlled offshore islands like Kinmen close to the mainland.
"We are willing to create a vast space for peaceful unification, but we will never leave any room for any sort of Taiwan independence separatist activities", he said.
In a speech commemorating the 40th anniversary of a message sent to Taiwan in 1979, in which Beijing called for unification and an end to military confrontation, Xi described unification under a "one country, two systems" approach that would "safeguard the interests and well-being of Taiwanese compatriots".
Ahead of Xi's speech Taiwanese President Tsai Ing-wen defended self-rule and said Beijing must respect its sovereignty.
The arrival marked the first time Taiwan has received 11 million overseas visitors in a single year, following 10.7 million visitor arrivals in 2017 and 2016, and 10.4 million visitors in 2015. As NPR's Beijing Correspondent Rob Schmitz has reported previously, Taiwan split from China in 1949 when the US -supported Chinese nationalist leadership fled after losing a civil war to communist forces.
Cross-strait issues on the part of Taiwan should be handled by the elected government which is monitored by Taiwanese people, said President Tsai.
An unfinished task for the ruling party on the mainland, Taiwan's unification has always been the ultimate goal for the Beijing leadership, although President Xi's predecessors, were more interested...
Tsai also blasted Xi for inviting political parties, groups and individuals from Taiwan to engage in talks on cross-strait political issues, saying that in a democracy, all political negotiations concerning cross-strait relations require a mandate from the people and must be subject to public scrutiny. Her remarks signaled that she would continue to take a firm line toward Beijing despite her recent election losses to Taiwan's more Beijing-friendly Kuomintang, Chiang's former party.
In an unusually harsh tone, Tsai said that the core reason her administration has never accepted the so-called "1992 consensus" is because Beijing's definition of "consensus" translates to "one China" and "one country, two systems". The rival Nationalists set up their own government on the island about 160 kilometres off the Chinese mainland.
Use of force against Taiwan would hurt China by inciting a response from Japan and the United States, Michael Tsai added.
In this December 1, 2018, file photo, U.S. President Donald Trump, right, and China's President Xi Jinping, left, attend their bilateral meeting at the G20 Summit in Buenos Aires, Argentina.
"I think she doesn't want the local officials to have private connections with Xi Jinping or any other PRC officials", Lee said. Over the past year, Beijing has ramped up efforts to isolate Taiwan, through pressuring worldwide companies and airlines to list the territory as part of mainland China.
Although President Xi said in his speech that unification with Taiwan through force is a possibility, Ding believes it is unlikely that Beijing would send troops to occupy Taiwan.
A day later on Wednesday, Xi appeared to fire back, saying that China had achieved "a great victory" against Taiwan's pro-independence movement.
"President Xi is anxious that the number of Taiwanese who identify themselves as Chinese is dropping".