Hundreds of migrants have broken through police lines on Hungary’s border with Serbia and are walking towards the capital, Budapest.
The Greek Government and the UN Refugee Agency have brought in extra staff and ships to deal with some 25,000 stranded migrants on the island of Lesbos.
A processing centre has also been set up on an abandoned football ground to help them get to Athens.
Violence erupted at a cornfield in Roszke where a poorly equipped migrant holding centre has been set up. Stones were thrown at officers, who responded with pepper spray.
About 300 migrants were later seen walking the wrong way along a motorway, escorted by police officers, though they later agreed to be taken by bus to another holding area.
Earlier, German Chancellor, Angela Merkel warned that the “breathtaking” flow of migrants into Germany would change the country in the coming years.
Hungary has become a flashpoint as thousands of migrants and refugees from the Middle East and Africa move North to claim asylum in Germany and other countries.
The country’s Defence Minister, Csaba Hende, resigned on Monday, reportedly over problems with the construction of a border fence meant to keep migrants out.
Local authorities have been overwhelmed by the migrants who have been forced to live in squalid conditions while Athens had already requested emergency EU assistance to deal with migrants arriving.