Serious incidents are taking place in Brussels outside the European Parliament building, with farmers setting fires, setting off smoke bombs and throwing objects at police.
Authorities responded with tear gas outside, while farmers caused damage during the clash.
At the same time, protesting farmers have blocked Avenue des Arts and Rue du Luxembourg with their tractors.
Thousands of farmers are in the Belgian capital to protest against the EU-Mercosur agreement.
They say they are concerned about the prospect of South American products entering the EU and about the reform of agricultural subsidies.
The EU-Mercosur agreement will create the world's largest free trade area and help the EU export more goods such as vehicles, machinery, wine and spirits to Latin America.
But farmers argue that it will also make it easier for beef, sugar, rice, honey and soy produced by their South American counterparts to enter Europe.
Shortly before midnight on Wednesday, this event had preceded the appearance of more than 100 tractors that blocked the Rue de la Loi, in front of the European Commission and European Council buildings, surprising the Authorities.
The mobilization occurred unexpectedly, as according to what was reported by the Belgian media, the farmers' arrival in the Belgian capital was expected for Thursday morning.
However, shortly after 11:00 p.m. local time, a procession of more than 100 tractors crossed Rue de la Loi, the main road that runs in front of the European Commission and Council buildings.
Traffic on Rue de la Loi was disrupted, with the road essentially "cut" in two, while police authorities took extensive countermeasures in an attempt to limit the presence of tractors and unblock the area.
According to information, some of the farmers had Luxembourg Square as their meeting place.
Strong police forces were deployed to the scene, with the help of helicopters and airstrikes, in order to prevent further escalation and maintain control around the European institutional buildings .