Hungarian police have fired tear gas after hundreds of migrants broke through a razor wire fence on the border with Serbia.
Some 1,500 refugees who had been hoping to travel through Hungary are now blocked by a 3.5m-high fence, where footage is now emerging of panicked men, women and children running away from police.
Sky News has witnessed a pregnant woman being stretchered from the scene and a young boy being carried away with tear gas in his eyes.
Water cannon is also being used, knocking some of the crowd off their feet.
Sky News' Colin Brazier is at the scene and said migrants were now throwing "really big rocks and house bricks" at police.
He said tempers had been flaring for several hours, with refugees left at the fence without food, water and information.
"It's very fractious," said Brazier. "There are young men who are really angry. It's a determined hard core of maybe a score - and behind them children and mothers."
Serbia has sent ambulances to the scene.
Prior to the outbreak of violence at the 110-mile fence this afternoon, police had detained 519 people who have tried to get through, and authorities have launched criminal proceedings against 46 people for allegedly illegally crossing the border.
Many migrants are now crossing into Croatia in an attempt to avoid Hungary - but there are fears they could set off landmines left over from the country's war with Yugoslavia in the 1990s.
Demining experts have been sent to a border area where hundreds of migrants began crossing from Serbia on Wednesday.
Other drivers were also told to take migrants on the same journey instead of heading north to Hungary, according to a reporter in Presevo.
Croatian Prime Minister Zoran Milanovic said his country is ready to accept migrants "regardless of their religion and the colour of their skin" and will help them pass through to Germany, Scandinavia or wherever else they want to go in Europe.
Elsewhere, Slovenia has said it will temporarily establish controls on its border with Hungary in the face of the biggest movement in people since the Second World War. Austria has done the same.
EU interior and justice ministers will hold another crisis meeting next week after failing to agree a quota plan to redistribute 120,000 migrants across the continent.
Hungary, Slovakia and the Czech Republic are among the states opposed to the idea.
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