Hundreds of Taiwanese protesters who support a controversial trade pact with China clashed with police Tuesday when they tried to push their way towards parliament, which has been occupied by students for two weeks.

The demonstrators, many wearing red headbands reading: "Want service trade pact, want jobs," shoved and shouted as they tried to push through a police cordon to confront the 200 students, who have barricaded themselves inside the parliament's main chamber in protest at the pact.

Police had strengthened the cordon, which lies one block away from the parliament building, after a pro-China group threatened to retake it from the students by force.

The protesters pushed hard against the 300-strong cordon several times, an AFP reporter at the scene said, but failed to break the security line, which included elite squads carrying shields.

They waved placards with the words "Illegal occupation of parliament" and "Students go home" while shouting similar slogans and blowing whistles.

The protesters also shouted "Lin Fei-fan coward!", "Chen Wei-ting coward!", referring to the two student leaders of the parliament seizure which began on March 18, the first ever in Taiwan's history.

A police line separated the pro-China activists from another group of hundreds of student protesters who had massed at the cordon.

The protest in favour of the pact was organised by Chang An-lo, a prominent Taiwanese gang leader also known as "White Wolf", who is on bail after being arrested on his return to Taiwan from China, where he had fled 17 years previously. He faces charges relating to organised crime.

He is known for his pro-China stance and is currently the chairman of a minor pro-unification party.

"The students have kidnapped the parliament which belongs to all people and they have held the parliament hostage ... they are bandits," Chang said.

- Security stepped up -

Hundreds of thousands of protesters took to the streets of Taipei on Sunday in a bid to pressure embattled President Ma Ying-jeou to retract the service trade pact and introduce a law to monitor all agreements with China.

Security was tight for Sunday's rally, following violent clashes when a group of protesters stormed the government headquarters on March 23. More than 100 people were injured when baton-wielding riot police used water cannon to disperse demonstrators.

Ma, who has sought closer ties with China since becoming the island's leader in 2008, has offered some concessions in the wake of recent confrontation, including a promise to pass a law to further scrutinise agreements with China.

However, he rejected the protesters' main demand -- that the service trade agreement signed with China in June last year be retracted, saying it could "cause too much damage to Taiwan".

Ma has warned that failure to ratify the pact would be a grave setback to Taiwan's efforts to seek more free trade agreements and avoid isolation as regional economic blocs emerge.

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

The deal is a follow-up agreement to a sweeping Economic Cooperation Framework Agreement signed in 2010 to reduce trade barriers between China and Taiwan.

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