ROSZKE, Hungary (Reuters) - Hundreds of migrants broke out of a Hungarian border camp and escaped from a stranded train on Friday as authorities appeared to lose control, despite taking a hard line in a country that has become a flashpoint of Europe's migrant crisis.

Hundreds more pushed past police barricades in the capital Budapest to set off for the western border on foot, even as Hungary tightened laws that the government said would effectively seal the southern border to migrants as of Sept 15.

Hungary has emerged as the main entry point for migrants reaching the EU by land across the Balkan peninsula, nearly all of them seeking to press on to richer and more generous countries further north and west, especially Germany.

The government in Budapest says it is implementing EU rules by forcing all of the migrants to register in the first EU country they reach.

Right-wing Prime Minister Viktor Orban, one of Europe's most outspoken critics of mass immigration, took to the airwaves to issue caustic warnings on Friday that Europeans could become a minority on their own continent.

But his government's plans for a crackdown appeared to be breaking down in the face of such large numbers headed for Germany, which has said Syrian refugees can register there regardless of where they enter the EU, suspending EU rules.

More than 140,000 migrants have been recorded entering Hungary so far this year through the EU's external border with Serbia, where Orban's government is building a 3.5 metre high wall. Countless others may have entered without registering.

On the border, police gave chase and halted traffic on a nearby motorway after some 300 migrants fled a crowded reception centre in Roszke near Serbia.

They were eventually caught, police said, but hundreds of officers in full riot gear and clutching shields continued to guard the camp. Some migrants were directed to buses to take them to other camps in an apparent attempt to prevent over-crowding.

In Budapest, about 500 migrants led by a Syrian refugee with one leg set out on foot from a sprawling campsite outside the Keleti railway station, where all trains to western Europe have been halted for days to prevent migrants from travelling. They broke through a police barricade on the main road west to Vienna shouting "Germany, Germany".

In Bicske, west of Budapest, some 500 migrants spent the night stranded on a train at the local railway station, refusing the demands of riot police that they disembark and go to a nearby migrant reception centre.

"No camp. No Hungary. Freedom train," someone had written with shaving foam on the side of the train. Hungary's MTI news agency later reported that some 300 had fled.

On Friday, lawmakers adopted some of a raft of measures creating "transit zones" on the border, where asylum seekers would be held until their requests are processed and deported if denied.

The measures introduce jail terms for those who cross the border without permission or damage the fence, and may eventually provide for the use of the army. Serbia appealed for EU funds to address a potential bottleneck of migrants.

Orban says he is trying to take control of Europe's migration crisis, the worst on the continent since the Yugoslav wars of the 1990s. But Budapest's hard line has produced scenes of chaos and desperation this week.

"We don't know what's going on," said Mr Ahmed Mahmoud, a 60-year-old Iraqi who said he was trying to reach his daughter in Belgium but had been stopped at the Bicske railway station.

"The police told us, get fingerprinted or face jail time. So we gave our fingerprints and they told us we can go. But we can't go to the west. I just want to see my child in Belgium."

The European Union normally allows free movement between the 26 countries of its Schengen border-free zone, but its rules require asylum seekers to register in the first country where they arrive and remain until they are processed.

Over 1,000 had been camped outside Budapest's Keleti railway station after Hungary cancelled trains to western Europe.

Orban took to the airwaves, saying Budapest was defending Europe's Schengen zone from a huge influx.

Hungary has hit out at Germany, which expects to receive 800,000 asylum seekers this year, for accepting requests from Syrians regardless of where they enter the EU.

Orban's government says this is spurring the flight, which he says poses a threat to Europe's "Christian values".

"Now we talk about hundreds of thousands but next year we will talk about millions and there is no end to this," Orban told public radio in a regular Friday interview.

"All of a sudden we will see that we are in a minority in our own continent."