Hundreds of Taiwanese activists were locked in a tense standoff with police Wednesday after they stormed parliament to try to stop the government ratifying a contentious trade agreement with China.

Around 200 protesters -- mostly young students -- broke through security barriers and took over parliament's main chamber on Tuesday night, the first such occupation of the building in the island's history.

They barricaded the doorways with piles of armchairs, blocking out hundreds of policemen who failed to push their way in early Wednesday.

Some 2,000 police including riot officers were mobilised over the course of the day to guard the parliament, said Taipei police chief Wang Cho-chun. They attempted to keep order as hundreds more protesters swarmed into the grounds.

Parliament speaker Wang Jin-pyng called for calm after 38 policemen were slightly injured following the early morning scuffle. At least ten civilians also received treatment for minor injuries. So far four people including three students have been arrested, police said.

"We will try to resolve this peacefully," speaker Wang told reporters.

President Ma Ying-jeou appeared unfazed and called on parliament to pass the trade pact.

"Otherwise the international community will think we do not have the resolve and we are not sincere and trustworthy," Ma told a meeting at ruling party headquarters.

Protesters vowed to stay in the chamber till Friday, the day lawmakers are set to hold a full session to review the pact, student leader Lin Fei-fan told AFP.

"We are not a mob and we are against violent means but scuffles could be inevitable if the police try to remove us, and the government should take full responsibility should that happen," Lin said.

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

But the protesters say the agreement will damage Taiwan's economy and leave it vulnerable to political pressure from China.

Inside the chamber demonstrators sang and waved placards, while stacking up large supplies of food and water.

They have accused the ruling Kuomintang party of "illegal" moves to ratify the agreement, and are demanding a clause-by-clause review of it.

"We oppose the Ma government for pushing for the pact without hearing opinions from all sides as it will affect many young people and the millions who work in the service industries," said student leader Lin.

Banners and placards reading "Sell out Taiwan" and "Surrender Pact" were unfurled outside parliament as more demonstrators gathered, chanting slogans demanding an apology from President Ma.

"I think Taiwan will be opening too much with the service trade pact and it is not fair for us. I don't want Taiwan to become the next Hong Kong to fall under the control of China," said student Shih Yi-chang.

The pact passed the first hurdle in parliament on Monday after it was approved by a committee in spite of opposition from some lawmakers.

The approval -- the first of three ratifications needed to pass the bill -- sparked a brawl between rival lawmakers and prompted three legislators from the opposition Democratic Progressive Party (DDP) to announce a 70-hour hunger strike.

The pact is one of the follow-up agreements to a sweeping Economic Cooperation Framework Agreement signed in 2010 to reduce trade barriers between China and Taiwan.

Under the latest deal, China will open 80 service sectors to Taiwanese companies, while Taiwan will allow Chinese investment in 64 sectors.

Ma has overseen a marked thaw in relations with China since he came to power in 2008, pledging to strengthen trade and tourism links.

China has emerged as the island's leading trade partner, while dozens of agreements between the two have been signed.

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