TAICHUNG: China's chief Taiwan negotiator flew into the island on Monday amid a push by Taipei for a sweeping trade pact with its giant neighbour in the face of vehement opposition protests.

Security was tight for the visit by Chen Yunlin, the head of a quasi-official Chinese body handling Taiwan relations in the absence of formal ties, as protesters gathered in the central city of Taichung.

Chen is due this week to hold his fourth meeting with his Taiwanese counterpart Chiang Pin-kung since Ma Ying-jeou of the pro-China Kuomintang (KMT) party became president of the island in May last year.

Ma has promised to lift Taiwan's crisis-battered economy by deepening exchanges with China, and his administration aims to sign a wide-ranging trade pact with the mainland some time next year.

Tens of thousands of banner-waving demonstrators had marched through Taichung on Sunday to protest at Chen's visit and the growing China ties, and more were gathering on Monday outside the envoy's hotel in Taichung.

A heavy police presence was in evidence outside the hotel, which was ringed by lines of barbed wire, with a total of 5,000 officers deployed to keep order during his visit.

Among the demonstrators were members of the Falungong spiritual movement, which has been banned as an "evil cult" for a decade in China and claims vicious persecution at the hands of the mainland authorities.

They were joined by pro-Tibet demonstrators carrying a large picture of the Himalayan region's exiled leader, the Dalai Lama, and its flag.

"The Tibetan people want to express their anger, because there are no human rights or freedom there," said one protester, 25-year-old Kelseng Lhundup.

Taiwan and China have been ruled separately since the end of a civil war in 1949, but Beijing claims the island as part of its territory and believes reunification is only a question of time.

Chen will hold formal talks with Chiang on Tuesday, and is expected to sign agreements on double taxation, agricultural quarantine and other economic issues.

He will attend a business conference on Wednesday and tour scenic spots Thursday before returning on Friday.

The Chinese envoy said last week that although the trade pact would not be a top agenda item, he expected general discussions on it while he is in Taichung.

The main opposition Democratic Progressive Party (DPP), which seeks formal independence from China, says the pact could make the island more reliant on the mainland, and would not even create the promised economic benefits.

"We oppose the Ma government striking any under-table deal with China," DPP spokesman Tsai Chi-chang told AFP.

"Right now many agreements with China are not monitored by parliament nor approved by the people, and they could hurt Taiwan's economy and cost many jobs."

On Sunday, the DPP organised a rally in Taichung to protest Chen's visit and the planned trade agreement. Tsai said about 100,000 people took part but police put the numbers at 30,000.