China's top negotiator on Taiwan affairs has arrived in Taipei for trade talks, which some Taiwanese fear could undermine the island's sovereignty.
Ahead of Chen Yunlin's arrival, tens of thousands of protesters rallied against the visit.
The two governments hope to sign a free-trade pact by early next year.
The visit comes as Taiwan debates how close a relationship it wants with its former rival China, which still claims the island as part of its territory.
Mr Chen is due to hold four days of talks on the proposed Economic Co-operation Framework Agreement (ECFA).
It is the fourth round of talks since Ma Ying-jeou - who is seen as being pro-China - became Taiwan's president last year.
The BBC's correspondent in Taiwan, Cindy Sui, says critics fear a free-trade pact will flood Taiwan with cheap Chinese products, cause massive job losses and undermine the island's sovereignty by making it too economically dependent on China.
The Taipei government, however, says Taiwan will be marginalised by China in global trade if it does not sign.
As he arrived for the talks in Taichung, Mr Chen hailed improving ties between China and Taiwan, but said he respected people's right to protest against his visit.
Demonstrators gathered outside his hotel on Monday, but numbers were much lower than the estimated 30,000 who had marched through Taichung on Sunday.
Mr Ma's pro-China stance once had a lot of support from the Taiwanese people, but his mishandling of the response to a devastating typhoon in August and other accusations of mistaken policies have dented his popularity.
Analysts say more people are now beginning to doubt his argument that closer economic ties with China will aid Taiwanese prosperity.
Taiwan and China have been governed separately since the end of a civil war in 1949.
Taiwan's opposition Democratic Progressive Party - which supports formal independence from China - made huge gains in local elections earlier this month.