By Kim Coghill

HONG KONG, Dec 18 (Reuters) - Hong Kong police braced for fresh demonstrations on Sunday after fighting running street battles with protesters trying to force their way into a building where a meeting of world trade ministers is taking place.

Organisers said they planned two huge marches later on the final day of the trade talks despite Saturday's violence which saw part of the city under siege and 96 people injured, including 23 police officers.

"The assembly is still on," said a spokeswoman from the Hong Kong People's Alliance, an umbrella group organising one of the anti-globalisation protests.

Police said late on Saturday that they had detained some 900 protesters after using tear gas to drive hundreds of them away from the harbourfront convention centre where the World Trade Organisation (WTO) meeting is being held.

On Sunday, however, a police spokeswoman said she was unsure how many people had been rounded up, saying "police operations are ongoing".

Police did not say if those who were detained or arrested would be charged or deported. Many of the protesters were South Korean farmers and workers who say free trade is ruining them.

The clashes were the heaviest since the WTO meeting began on Tuesday. It was the worst violence in Hong Kong since 1989 protests following China's bloody crackdown on democracy protesters in Tiananmen Square in Beijing.

Yet the fighting was less intense than that which marred the 1999 WTO conference in Seattle, the scene of huge and violent demonstrations against trade globalisation.

As dawn broke on Sunday a group of more than 100 diehard protesters was staging a sit-in on a road a few blocks from the convention centre, surrounded by riot police.

Some streets in the Wanchai entertainment district not far from the city centre were reopened to traffic after pitched battles for much of Saturday night between protesters and police.

Protesters wielding bamboo sticks and iron poles began storming heavily fortified police lines in late afternoon, breaking through ranks of police who used pepper spray, batons and blasts of water from fire hoses to try to beat them back.

At one point, they were only about 30 metres (yards) from the convention centre, Reuters reporters said.

Inside the building, trade ministers were locked in talks well into the early morning, trying to find an elusive world trade deal which critics say will hurt the world's poor.