At least 100,000 people have marched in Taiwan in support of a government plan to hold a referendum on joining the UN under the name Taiwan.
China has blocked Taiwan's past attempts to gain a UN seat
The UN has rejected previous bids from the island to join the body under its official name, Republic of China.
The bids anger Beijing, which sees Taiwan as a breakaway province. China has vowed to use force if Taiwan took steps towards formal independence.
China's opposition means Taiwan's bids for a UN seat are certain to fail.
Ruled by separate governments since end of Chinese civil war in 1949
China considers the island part of its territory
China has offered a "one country, two systems" solution, like Hong Kong
Most people in Taiwan support status quo
The march, in the southern city of Kaohsiung, attracted hundreds of thousands of people according to organisers, while police said 100,000 took part.
Kaohsiung is a power base for the ruling Democratic Progressive Party's (DPP) presidential candidate Frank Hsieh.
The government intends to time the referendum with the presidential vote next March.
Analysts say the DPP hopes the referendum debate will shore up its support in the elections.
"Give Taiwan a chance to join the UN," Mr Hsieh told a crowd in Kaohsiung before the march.
Independence-leaning President Chen Shui-bian said Taiwan had "every right to be a full UN member, standing on equal footing with other member states".
The opposition Kuomintang (KMT) also favours a referendum on joining the UN, but under the island's official name Republic of China.
The KMT held a separate rally for the central city of Taichung attended by its presidential candidate Ma Ying-jeou which attracted an estimated 50,000 people.
The UN switched its recognition from Taiwan to mainland China in 1971.
China's President Hu Jintao has warned that the plan could result in a "possibly dangerous period" for the region.
The United States has also warned that the move is unnecessarily provocative and could heighten tensions in the region.
Most UN members have diplomatic ties with China and would not want to anger Beijing by backing Taiwan's UN application.