The signing of a trade deal between the EU and South American bloc Mercosur will be postponed to January, officials said on Thursday, after farmers staged a show of force against the pact outside a Brussels leaders' summit.

Mercosur nations were notified of the move, which came after EU plans to seal the pact this week were upended by heavyweights France and Italy demanding a delay, a European Commission spokeswoman said.

The EU-Mercosur deal would create the world's biggest free-trade area and help the 27-nation bloc to export more vehicles, machinery, wines and spirits to Latin America at a time of global trade tensions.

But Paris and Rome want more robust protections for their farmers, who fear being undercut by a flow of cheaper goods from agricultural giant Brazil and its neighbours.

Thousands of farmers flooded the Belgian capital on Thursday – rolling around 1,000 honking tractors into the city – as the deal loomed large over the European leaders' gathering.

Having initially reacted with a now-or-never ultimatum to its EU partners, Brazil opened the door on Thursday to delaying the deal's signature to allow time to win over the holdouts.

Brazil's President Luiz Inacio Lula da Silva said Italian Prime Minister Giorgia Meloni had asked him for "patience" and had indicated that Italy would eventually be ready for the agreement.

EU chief Ursula von der Leyen subsequently informed EU leaders in Brussels that the signing would be pushed back to "early January", the commission spokeswoman said. (AFP)