Leaders from 34 nations have begun arriving in Argentina for the fourth two-day Summit of the Americas.
More than 8,000 police officers are guarding the venue
They are meeting in the coastal resort of Mar del Plata amid much uncertainty about what can be achieved on the summit's main aim of job creation.
There are deep divisions over free trade, with the US championing it as the best way to relieve poverty.
President George W Bush is among those attending the talks. He is expected to be targeted by left-wing protesters.
Thousands of people are due to stage a protest rally that will be addressed by Venezuelan President Hugo Chavez.
Argentine former football legend Diego Maradona and Bolivian left-wing presidential candidate Evo Morales will also take part in Friday's demonstration.
A train that will take Maradona and dozens of other well-known people such as Bosnian filmmaker Emir Kusturica and Cuban singer Silvio Rodriguez is to leave Buenos Aires late on Thursday.
The train dubbed "Alba Express" will be joined by road by hundreds of buses carrying members of political and social organisations.
The caravan is expected to arrive in Mar del Plata early on Friday. Anti-globalisation and anti-US activists have been holding a parallel "People's Summit" there.
Foreign ministers from the region have been holding talks ahead of the summit.
More than 8,000 police officers are guarding the venue of the Summit of the Americas.
Mr Bush has already arrived to Mar del Plata
The rivalry between Mr Bush and Mr Chavez is expected to dominate the meeting.
In his keynote speech, Mr Bush will argue that the way to guarantee prosperity is by encouraging free trade and a flourishing private sector and by deepening democracy, the BBC's Jamie Coomarasamy in Mar del Plata reports.
Although, Mr Bush has acknowledged that efforts to form a Free Trade Area of the Americas have stalled, our correspondent says.
The Venezuelan government has said that it will reject any summit declaration which contains references to free trade in the Americas.
Some 96 million people in the region are surviving on less than $1 per day, according to the United Nations.