A Eurostar train is waiting to cross from the Channel to England, at the Calais-Frethun train station in northern France, on Wednesday.

Reuters/Calais, France/Budapest

Hundreds of migrants poured overnight onto the high-speed railway linking Paris with London near the French port of Calais, stranding thousands of passengers in darkness for hours aboard Eurostar trains.

At the EU's opposite end, another angry crowd camped outside a Budapest train station demanding to board trains for Germany, as Europe's asylum system crumbled under the continent's biggest migration crisis since the 1990s Balkan wars.

Hundreds of thousands of refugees fleeing wars and economic migrants escaping poverty have arrived in the European Union in an unprecedented wave that has confounded EU leaders and fed the rise of right wing populists.

Nearly all first reach the EU's eastern and southern edges and then press on illegally for richer and more generous EU countries further north and west.

The EU's executive European Commission promised to unveil a new policy next week to make it easier to process asylum claims, distinguish bona fide refugees from other migrants, send those from safe countries home and distribute those with genuine asylum claims among the bloc's 28 members.

Free movement

Meanwhile, authorities have struggled to enforce rules which ordinarily allow free movement within the EU but not to undocumented migrants.

Hundreds took to the tracks around France's Calais-Frethun station, the latest target for those trying to reach Britain, which many regard as a better place to live than countries on the continent.

Rail operator SNCF was forced to halt services near the entrance to the Channel Tunnel. Three Eurostar trains were blocked overnight and eventually continued to London early on Wednesday, while two returned to their departure stations.

Passengers on one London-bound train, which stopped less than a mile from the tunnel, were told at one point to keep quiet and listen for people on the roof. A helicopter with a searchlight circled as guards walked the tracks.

With the power out, passengers sat in stifling darkness for nearly four hours. A woman in business class wept.

Eurostar later pulled the train back to Calais, where passengers disembarked for fresh air and bottled water.

About 3,000 to 4,000 migrants from the Middle East, Asia and Africa camp near Calais, dodging police as they try to board trains and trucks heading to Britain through the tunnel or on ferries. They have disrupted passenger and freight transport between Britain and France throughout the summer.

A spokeswoman for Eurotunnel, which operates the railway tunnel beneath the channel, said that as security has been tightened at Calais port and the tunnel entrance, migrants have sought new entry points such as Calais-Frethun, about 5 km inland, beyond a zone controlled by Eurotunnel.

Freedom! freedom!

In Hungary, hundreds of migrants protested in front of Budapest's Keleti Railway Terminus shouting "Freedom, freedom!" and demanding to be let onto trains bound for Germany.

More than 2,000 migrants, including families with children, were waiting in the square at the station while Hungarians with IDs and foreigners with valid passports could board the trains.

Germany, which is prepared to take by far the greatest number of refugees, has begun accepting asylum claims from Syrians regardless of where they entered the EU, even though undocumented migrants are barred from travel across the bloc. That has caused confusion for neighbouring countries, which have alternated between letting migrants through and halting them.

Hungary, the main arrival point for those crossing the Balkans by land, allowed thousands to board trains for Germany on Monday but has since called a halt, creating chaos at the rail station. A government spokesman said Hungary would observe EU rules which bar travel by those without valid documents.

"I want my freedom, I have been on the road for a very long time, and now I am in the European Union, and I want my freedom," said Sanil Khan, 32, leader of a group of about 100 young men who marched behind a cardboard cutout Afghan flag in a tight formation.

The men were joined by hundreds of others, who broke into loud cheers and chants of "Freedom, freedom!" and "Germany, Germany!"

Migration crisis

The migration crisis has confounded the EU, which is committed to the principle of accepting refugees fleeing real danger but has no mechanism to compel its 28 member states to share out the burden.

Countries like Italy, Greece and Hungary, where most migrants arrive, say they need more help from EU partners. Germany has been the most forthcoming, with plans to accept hundreds of thousands of refugees this year alone, adding €3.3bn ($3.7bn) to its welfare bill next year.

But that has caused railway chaos for neighbours. Berlin says that despite its decision to accept asylum applications from Syrians who arrive elsewhere in the EU, other EU states must still demand migrants remain where they first register.

At the opposite end of the spectrum of openness is Britain, which so far has accepted just 216 Syrian refugees under a scheme in partnership with the UN, as well as around 5,000 that managed to reach Britain and apply on their own.