Why Europe's tough migrant trail is still so busy

Thousands of people are still making the difficult journey across Europe every day despite the approach of winter, taking huge risks to flee war and poverty in the continent's worst migrant crisis since World War II.

More than 670,000 people this year have made the dangerous journey across Mediterranean, this year, then faced gruelling overland marches and long train trips to borders which have sometimes been closed, forcing them to find alternative routes.

Here is an overview of the journey, the people and the countries involved:

- The Syrian wave -

Migration has been a challenge for Europe for years but the current wave has been sparked by the escalation of the Syrian civil war, which has claimed 250,000 lives and created four million refugees since it broke out in 2011.

"We face the biggest refugee and migration crisis since World War II," UN chief Ban Ki-Moon said last month, echoing top European officials.

The burden has so far fallen mainly on Syria's neighbours Lebanon, Jordan and Turkey who have taken in the largest number of refugees, with Turkey hosting more than 2.2 million of them.

Conditions have deteriorated markedly in recent months, UN refugee agency (UNHCR) chief Antonio Guterres said recently, with funding for camps falling and many refugees unable to work due to restrictions in host countries.

With no sign of the war ending and Russia joining the fray with air strikes, more and more Syrians are leaving for Europe to build new lives.

- Who are they -

Migrant movements to Europe have tripled between 2014 and 2015, International Organisation for Migration and UNHCR figures show.

A total of 670,000 migrants have arrived in Europe by sea in 2015 so far, according to IOM figures. They are a mix of asylum seekers from war-torn or repressive countries such as Syria, Iraq and Eritrea, as well as economic migrants.

Of the estimated half a million who have arrived in Greece alone since the start of the year, 288,000 of them were Syrians, 77,000 Afghans, 22,000 Iraqis and 14,000 Pakistanis, the IOM said.

In Italy, the EU country which has seen the next biggest number of arrivals, there were 36,000 Eritreans, 18,000 Nigerians and 10,000 Somalis.

- Winter is coming -

Unlike previous years when the flow of migrants slowed to a trickle during winter, the change in seasons is unlikely to have a major effect this year, experts say.

This is partly because a new wave of people are expected to flee Syria, with the Syrian Observatory for Human Rights warning that around 100,000 people are on the move following a Russian-backed Syrian army offensive on Aleppo.

Syrian refugees have increasingly lost hope of returning home and also sense that Europe's doors will soon be shut "so they think 'better get moving'," says Louisa Vinton, a UN official in Macedonia.

Although in previous years the main crossing was the long sea route from Libya to Italy, this year more refugees have braved the far shorter but still dangerous crossing from Turkey to Greece.

- Changing routes -

The routes they take towards western Europe are constantly shifting.

The huge risks involved in crossing the Mediterranean from Libya to Italy -- more than 2,800 of the 3,100 migrants who died at sea in 2015 perished making that voyage -- and an EU naval mission targeting people smugglers have helped cut numbers on that route.

As a result, the main influx of newcomers are crossing the Aegean Sea from Turkey to Greece, then travelling up through the Western Balkans. After crossing Greece, they travel by train through Macedonia and Serbia towards the eastern flanks of the European Union, where they cross on foot.

But the Balkan route is in flux: after Hungary shut its borders, people turned westwards through Croatia and then on to Slovenia, the latest country to buckle under the weight of the numbers of newcomers.

- What is the EU doing? -

The EU lurched into action after a major shipwreck in April that left 700 people dead but despite four summits dedicated to migration it has struggled to coordinate a unified response.

It spent months arguing over a plan to share 160,000 refugees from Greece and Italy around the rest of the EU.

Now EU leaders have agreed to focus on strengthening the bloc's external borders, reasoning that unless it does so, its internal passport-free Schengen zone will be at risk of collapse.

Other steps include so-called "hotspots" -- reception centres where new arrivals can be more quickly processed with EU help -- and deals to repatriate economic migrants to their countries of origin, mainly Africa.

The EU has also launched an as yet unsuccessful diplomatic bid to persuade a reluctant Turkey and other transit countries to keep the migrants on their soil.