President Xi's statement came after Chinese air force mounted four straight days of incursions into Taiwan's air defence identification zone from October 1, involving close to 150 aircraft, though those missions have since ended.
Chinese leader Xi Jinping has said reunification with Taiwan must happen and will happen peacefully, despite a ratcheting-up of China's threats to attack the island.
Xi spoke on at an official celebration in Beijing's Great Hall of the People the focused largely on the need for the ruling Communist Party to continue to lead China as the country rises in power and influence.
“Reunification of the nation must be realised, and will definitely be realised,” Xi said. “Reunification through a peaceful manner is the most in line with the overall interest of the Chinese nation, including Taiwan compatriots.”
The celebration was in honour of the 110th anniversary of the Chinese revolution in 1911 leading to the overthrow of the Qing dynasty and establishment of the Republic of China led by Sun Yat-sen.
October 10 is celebrated in Taiwan as National Day and Xi's address touched on common aspirations for a unified future, despite the stark differences between China's authoritarian one-party system and Taiwan's vibrant multi-party democracy.
Xi's remarks came just days after the Chinese military sent a record number of military aircraft flying towards Taiwan in exercises that the self-ruled island has called a threat.
Responding to Xi's statement, Taiwan presidential office said the country's future "rests in the hands of its people", adding public opinion in Taiwan rejects "one country, two systems."
Over the course of four days, starting last week, the People's Liberation Army flew fighter jets, bombers and airborne early warning aircraft 149 times towards Taiwan, with the largest manoeuvre involving 52 jets at once.
Taiwan and China split in 1949 amid civil war, with the then ruling Nationalist Party fleeing to the island as Mao Zedong's Communists swept to power on the mainland.
Since then, Taiwan has been self-ruled, but its sovereignty is denied by Beijing, which has refused to renounce the option of using force to bring the island under its control.
Beijing has also sought to isolate Taiwan internationally by barring it from the United Nations and other international organisations and opposing official contacts between its government and nations that recognise China, especially the United States, which is legally bound to consider threats against Taipei a matter of “grave concern."
“Taiwanese separatism is the biggest obstacle to the motherland's reunification,” Xi added, saying those who advocated for independence would be “condemned by history.”