Dozens of people were detained in Taipei late Sunday after violent clashes erupted between police and protesters, following the Taiwanese president's refusal to scrap a contentious trade agreement with China.

Hundreds of protesters who had been staging a demonstration against the trade pact pushed past riot police in full gear to storm the government headquarters, before the crowd was dispersed shortly after midnight.

Tensions exploded into the open on Tuesday when around 200 demonstrators, mostly young students, broke through security barriers and took over parliament's main chamber, the first such occupation of the building in the island's history.

President Ma Ying-jeou moved Sunday to denounce the "illegal" occupation of parliament by students opposed to the trade agreement's ratification.

Local TVBS news network showed protesters pulling down barbed wire barricades surrounding the government building, with some using ladders to break into offices on the second floor of the building.

The network showed clashes between protesters and police holding shields, as well as an injured male protester lying on the ground being attended to by medical personnel.

The TV footage also showed blood streaming down the face of a male protester while citing hospital sources as saying more than 17 people were injured and more than 50 detained for questioning.

Student leader Lin Fei-fan called for calm: "I know many people were disappointed at what Ma said, but we have to maintain peace and non-violence principle."

During a press conference earlier in the day, President Ma said: "The student group have been occupying parliament's main chamber in a manner violating the law, paralysing the legislature's operation for five days."

"I must say that (the pact) is completely for the sake of Taiwan's economic future."

Ma warned of trade-reliant Taiwan being marginalised without the China agreement and similar pacts with other countries, as regional economic blocs emerge.

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

Opponents say it will damage Taiwan's economy and leave it vulnerable to political pressure from China, allegations rejected by Ma's ruling Kuomintang party.

- 'Let us calm down' -

Ma, who initiated Taipei's detente with Beijing after coming to power in 2008, refused to back down Sunday and termed the occupation of parliament as illegal.

"Let us calm down and think carefully. Is this the democracy we want? Do we have to do in this way, risking the rule of law," he said.

"As the president of the Republic of China (Taiwan's official title), I have to insist on the rule of law while safeguarding democracy. This is the fundamental and unswerving position of the government."

Protesters responded by saying the Kuomintang's push in parliament to ratify the agreement had been illegal, and this entitled them to occupy the legislature.

"The Ma government broke the law first. That was the reason why tens of thousands of people are taking to the streets," student leader Lin said in a statement.

Thousands of opponents of the deal have rallied outside parliament.

"The occupation of parliament is aimed to underscore the ridiculousness of the present (parliamentary) mechanism," Lin said.

"In a democratic country, people have the right to decide the country's future."

Hundreds of police attempted to end the occupation hours after it began, but failed to push their way through piles of armchairs barricading the doorways.

Premier Jiang Yi-huah walked to parliament Saturday to hold the first direct dialogue between the government and protesters, but failed to reach a breakthrough.

Jiang rejected demands to withdraw the agreement but said he would support calls for its thorough review by parliament.

The pact, signed in July, passed its first parliamentary hurdle on Monday last week when it was approved by a committee, but the opposition insisted the approval process was illegal.

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.

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

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