Student activists Thursday ended an unprecedented three-week occupation of Taiwan's parliament in protest at a service trade pact with China, but threatened more action unless their demands are met.

"The departure does not mean we are giving up," said student leader Lin Fei-fan, shortly before dozens of demonstrators clad in black T-shirts walked out of the building at around 6 pm (1000 GMT).

The protesters' next moves "could be more comprehensive" unless guarantees given by Taiwan's ruling China-friendly Kuomintang party are honoured, he told a press briefing.

Referring to the need closely to monitor developments, Lin said: "We came here with ideals, now we leave with more burden".

Holding sunflowers which are the symbol of their movement, the protesters -- mostly young students -- were warmly greeted by thousands of supporters as they emerged from the building.

Opponents see the services trade deal as damaging Taiwan's economy and leaving it vulnerable to political pressure from China, which still claims the island more than 60 years after the two governments separated.

In Taiwan's first such protest, the demonstrators broke security lines and occupied the main chamber of parliament on March 18, using huge stacks of armchairs to barricade themselves in.

The standoff with police came to an end after parliament's Speaker Wang Jin-pyng, a political heavyweight from the Kuomintang, met the students and offered a concession.

Wang pledged not to preside over further debate about the services trade pact until a law has been introduced to monitor such agreements with China -- a key demand of the protesters.

The demonstrators earlier Thursday had dismantled the piles of armchairs, packed up their sleeping bags, taken down posters and even repainted the walls.

With their departure, parliament will resume operations Friday.

Legislators will begin by reviewing seven versions of the bill which have been tabled, including one from the protesters and another from the major opposition Democratic Progressive Party which supported the occupation.

The protesters have urged the Kuomintang government to retract the services trade deal, a demand which President Ma Ying-jeou has flatly rejected.

Their action drew large crowds of supporters, with more than 10,000 gathered outside at one point.

There were violent clashes on March 23 when baton-wielding police turned water cannon on other demonstrators who had stormed the nearby government headquarters.

The pact is designed to further open up trade in services between China and Taiwan, which split 65 years ago after a civil war.

It is a follow-up agreement to a sweeping Economic Cooperation Framework Agreement signed in 2010 to reduce trade barriers between the two.

Ma, who has pursued closer ties with China since coming to power in 2008, has said failure to ratify the deal would be a grave setback to efforts by export-reliant Taiwan to boost trade.

Ma has overseen a marked thaw in relations with Beijing since he came to power pledging to strengthen trade and tourism links.

He was re-elected in January 2012 but is battling to shore up his popularity, with his approval ratings currently sitting at around only 10 to 15 percent.

China still considers Taiwan part of its territory awaiting reunification -- by force if necessary.