Dairy farmers sprayed thousands of litres of fresh milk at the EU parliament in Brussels in protest at what they say are excessive milk quotas and prices below the cost of production.
Hundreds of farmers from across Europe took up position with tractors in a park near the European Commission and at a square in front of the parliament building in the early afternoon on Monday, after blocking traffic along several of Brussels' busiest streets.
They then turned their hoses on parliament, a collection of vast marble, glass and steel buildings on a downtown city square, unleashing torrents of milk, some of it raining down on police and passers-by.
Afterwards, they set alight barrels of hay and a pile of tyres, sending plumes of black smoke billowing into the sky.
They planned to stay put outside parliament until Tuesday afternoon.
The European Milk Board, which co-ordinated the two-day protest, said prices with current quotas were putting small
farmers out of business.
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In Belgium, for example, the board said the wholesale price for a litre of milk was 0.26 euros, but the cost of producing it is 0.40 euros.
The EU is the world's largest milk producer and spends more than 40 per cent of its annual 130 billion euro ($173bn) budget paying subsidies and other forms of financial support to farmers, including those in the diary industry.
It sets an annual milk production quota - which sits at around 130 million tonnes, too much for EU-consumption - but has agreed to phase that out by 2015.
Farmers have held similar protests in the past, including one in 2009 which led to a small increase in wholesale prices.
On Monday, tractors came from across Belgium as well as neighbouring France, Germany, Luxembourg and the Netherlands.
Among a total of nearly 2,500 farmers, around 100 came from Poland, with many other nationalities also present.