Timeline: Key dates in Europe's migrant crisis

Austria and Slovakia followed Germany's lead in reinstating border controls as Europe struggles to cope with the continent's worst refugee crisis since World War II.

More than 430,000 migrants and refugees have risked their lives since the beginning of the year making the treacherous crossing across the Mediterranean to Europe, with nearly 2,800 dying en route, according to the International Organisation for Migration.

Many of those trying to reach Europe are Syrians fleeing the war at home. 

Here are key dates in the crisis:

April 23: EU leaders triple the bloc's budget for sea rescues and mull military action against human smugglers in Libya after 1,200 migrants drown in a single week off Libya.

May 13: The EU's executive Commission proposes that countries share responsibility for housing thousands of refugees.

July 20: EU leaders agree to a voluntary scheme to accept 32,256 migrants from Italy and Greece, falling short of a target of 40,000.

July 30: A migrant in Calais, France, is the 10^th to die in two months while trying to make it across the Channel to England.

August 27: The decomposing bodies of 71 Syrians are found in an abandoned lorry in Austria. A day earlier, 52 corpses were found in the hold of a boat off Libya.

September 2: The picture of a three-year-old Syrian boy's body, washed ashore on a Turkish beach after a migrant boat sank, prompts an outpouring of public sympathy for refugees.

September 3: Budapest's main train station is reopened to migrants after a two-day closure and standoff. Hundreds board trains headed for the Austrian border.

September 7: France agrees to take in 24,000 refugees over two years, while Britain agrees to take in 20,000 Syrians over five years. Berlin earmarks six billion euros extra to help the refugees.

September 9: European Commission chief Jean-Claude Juncker urges member states to take in 120,000 refugees from overstretched Italy, Greece and Hungary, combined with a similar scheme for 40,000 refugees in Italy and Greece that he unveiled in May.

September 11: Several European countries come out against the quota system advocated by Berlin and Brussels.

September 13: A record 5,809 people arrive in Hungary amid a rush to get in before a fence along the frontier with Serbia is completed.

Germany reinstates passport checks on the border with Austria, in a shock U-turn on the government's earlier policy of opening its doors to Syrian refugees.

Off the Greek coast, 34 migrants - including four babies and 11 children - drown when their overcrowded boat capsizes.

September 14: Austria and Slovakia say they too are reintroducing border controls.

Germany warns it could face up to one million arrivals this year.

EU member states approve plans for military action against people smugglers in the Mediterranean, seizing and if necessary destroying boats to break up the networks operating out of Libya.