(Recasts, adds details)
By Michael Gold
TAIPEI, March 23 (Reuters) - Hundreds of demonstrators occupied part of Taiwan's government headquarters on Sunday night in protest against a controversial trade pact with mainland China.
President Ma Ying-jeou says the pact with Taiwan's main export market is essential for the island's prosperity.
However, the main opposition party says it could hurt small service companies, and many others are reluctant to let China expand its influence over a fiercely independent and democratic territory that China still sees as a renegade province.
Television footage showed protesters and police scuffling after several people forced their way into the building.
The reports said the demonstrators had barricaded doors and windows with tables and chairs and seized the computer of the head of the presidential cabinet, and that at least 13 people had been injured.
Opponents of the pact forced their way into the island's parliament last Tuesday, and have taken to the surrounding streets every day since then.
Parliamentary approval of the agreement on April 8 would open 80 of China's service sectors to Taiwan and 64 Taiwanese sectors to China.
"This is completely for the sake of Taiwan's economic future," said Ma, who since 2008 has signed a series of landmark trade and economic agreements with China.
Ma and his ruling Kuomintang Party say Taiwan needs the pact not only to maintain the competitiveness of its exports but also as an entry ticket to the Trans-Pacific Partnership, a broad trade deal among 12 countries, spearheaded by the United States.
Ma said he understood the passion of the mostly young protesters, as Taiwan "can only have a future if young people care about the country and are brave enough to participate".
But he said their occupation was illegal and hampering the work of government.
"Are we not proud of Taiwan's democracy and rule of law?" Ma said. "If there is no rule of law, democracy cannot be protected."
Taiwan made a peaceful transition from dictatorship to democracy in the late 1980s, and now boasts one of Asia's most freewheeling democracies. Fights in parliament are common and protests are almost a daily occurrence.
Taiwan and China have been ruled separately since the Communists took power on the mainland in 1949, though relations have warmed considerably since the China-friendly Ma won the presidency in 2008 and secured re-election in 2012. (Editing by Kevin Liffey)