Hundreds of students protesting against an Apec summit in Chile to be attended by US President George W Bush have clashed with riot police.
The students oppose a visit by President Bush at the weekend
The unauthorised student march was met with water cannon and tear gas.
The students blocked traffic and built barricades. Estimates of the number detained ranged from 120 to 500.
Counter-terrorism and trade were expected to dominate discussion as ministers from the 21 Asian-Pacific nations met.
The meeting precedes the weekend's Asia Pacific Economic Cooperation (Apec) Forum, attended by national leaders.
There is tight security ahead of the summit, with about 4,000 police deployed in Santiago, a city of about 5.5 million.
La Tercera newspaper said the police began dispersing the students as they met ahead of a planned march several kilometres away from the Apec convention centre on Wednesday.
They fired water cannon and teargas, prompting local shops to hurriedly close.
The students regrouped and began taking banners out of their bags only to be forcibly dispersed again.
One report said they built barricades down side streets with rubbish bins and threw paint bombs at police.
The students said they opposed, among other things, the war in Iraq and neo-liberal capitalist policies.
"I oppose the Apec summit because they only come to drink wine and talk, when the decisions have already been made," Caterina Paz told La Tercera.
"And besides, Bush is the icon of international terrorism."
La Tercera estimated 120 students had been detained. Other local media put the figure closer to 500.
Despite the announcement that he is leaving his post soon, Secretary of State Colin Powell will still represent the US at the annual ministerial meeting.
The conference will run for two days and then issue a lengthy declaration.
A draft copy of the statement, obtained by the BBC and two Australian newspapers, shows a major emphasis on counter terrorism.
The draft declaration calls for new restrictions to stop terrorists obtaining dangerous items such as manned portable air defence systems.
These are shoulder-fired missiles that can bring down planes as they take off or land.
It has become tradition for Apec leaders to appear in local costume
The document also warns of possible terrorist attacks through toxic or hazardous material hidden in food.
Security issues have become increasingly important to Apec in recent years, but there is a focus on trade.
The ministers are due to declare their support for recent efforts to try and restart global trade talks.
But they are also likely to warn that agricultural protection remains a key stumbling block.
The 21 Apec economies, which include China, Russia and Japan, collectively represent 47% of world trade.
At the end of every Apec summit it has become tradition for leaders to appear in traditional local costume.
This time, a senior foreign ministry official told AFP news agency, the leaders would be given poncho-like "chamantos" to wear.