GENEVA/BUDAPEST: The United Nations' refugee chief called on Friday for Europe to mobilise its "full force" in tackling its migrant crisis, just as Hungary's right-wing leader told Europeans they risk becoming a minority on their own continent.

Declaring that the European Union faces a "defining moment", the head of the U.N. refugee agency Antonio Guterres said a divided bloc would benefit only smugglers and people traffickers.

His appeal for EU states to do more in helping migrants - many of them refugees fleeing the Syrian civil war - contrasted with the tough line from Hungarian Prime Minister Viktor Orban, who warned about the consequences of "a mass inflow of people", possibly numbering tens of millions.

Hundreds of thousands of people trying to escape conflict and poverty are making the dangerous and arduous journey by sea and land, heading towards wealthy northern European countries such as Germany in the hope of finding safety and a new life.

But many migrants are stuck en route, including in Hungary where hundreds woke up on Friday after a night on a packed train stranded at a station west of Budapest, refusing to go to a nearby camp to process asylum seekers.

Guterres said the EU needed to help more migrants enter legally and provide about 200,000 relocation places, according to a preliminary estimate, as well as support countries under pressure such as Greece, Italy and Hungary.

"It now has no other choice but to mobilise full force around this crisis. The only way to solve this problem is for the Union and all member states to implement a common strategy, based on responsibility, solidarity and trust," he said in a statement.

More than 300,000 people have risked their lives this year trying to cross the Mediterranean, and more than 2,600 people have died doing so.

Guterres said the image of a drowned Syrian toddler washed up on a Turkish beach which has swept across social media this week had "stirred the hearts of the world public", but said the EU had so far failed to find a collective common response.

Aylan Kurdi, aged 3, was buried in the Syrian town of Kobani on Friday alongside his 5-year-old brother and their mother, both of whom had also drowned at the same time.

Turkish President Tayyip Erdogan, across whose country many of the refugees trek as they head north and west via the Greek islands, has also appealed to developed countries, notably in Europe, "to be more sensitive in the face of human dramas".

Turkish authorities stopped 57 people trying to cross to the Greek island of Kos on Thursday night, as migrants remained undeterred by the boy's drowning on the same route.

"MINORITY IN OUR OWN CONTINENT"

Erdogan's appeal drew little sympathy from Hungary's Orban, who defended his government's hardline stand on the crisis.

"The reality is that Europe is threatened by a mass inflow of people. Many tens of millions of people could come to Europe," he said. "Now we talk about hundreds of thousands but next year we will talk about millions and there is no end to this."

"All of a sudden we will see that we are in minority in our own continent," Orban told public radio.

Hungary has hit out at Germany, the most popular destination among the migrants, for saying it would accept asylum requests from Syria regardless of where they entered the EU.

With the pressure growing, British Prime Minister David Cameron said his country would take "thousands more" refugees from Syria. Until now, Britain has taken in only small numbers of Syrian refugees, drawing criticism at home and aboard.

German Chancellor Angela Merkel has vowed her country will not tolerate xenophobia, but a poll for ARD television showed her popularity has dropped abruptly over her handling of the migrant crisis.

Merkel, who was criticised for being slow to condemn violent protests against refugees in an east German town last month, saw her approval ratings slip by 4 points from the previous month to 63 percent in the Infratest Dimap survey.

That said, most European leaders struggling to revive their economies could only dream of a 63 percent approval rating.

A record 104,460 asylum seekers entered Germany in August and the country expects about 800,000 people in total to file for asylum this year, four times last year's level.

Migrants aboard the train near Budapest are worried that registering as asylum seekers in Hungary will prevent them heading to Germany. They wrote on the side of the train: "No camp. No Hungary. Freedom train".

They wrestled with police on Thursday, some throwing themselves on the tracks insisting they be allowed to remain on the train bound for a border town near Austria.

The train had left Budapest on Thursday morning after a two-day standoff at the city's main railway station as police barred entry to some 2,000 migrants. Hungary says they must be registered, as per EU rules, but many refuse.