* Police and army sealed border Thursday
* Fired tear gas and stun grenades to drive crowds back
* Thousands spent cold night under open skies (Updates with buses, crowds)
By Fatos Bytyci
GEVGELIJA, Macedonia, Aug 22 (Reuters) - Thousands of migrants stormed across Macedonia's border on Saturday, overwhelming security forces who threw stun grenades and lashed out with batons in what became a futile bid to stem their flow through the Balkans to western Europe.
Some had spent days in the open with little or no access to food or water after Macedonia on Thursday declared a state of emergency and sealed its borders to migrants, many of them refugees from war in Syria and other conflicts in the Middle East.
By nightfall, just a couple of hundred people remained in a rain-soaked no-man's land. Riot police were also present, but some migrants appeared to simply stroll over the border to a hoard of buses that had arrived at the town of Gevgelija.
There was no official word that Macedonia had abandoned its bid to keep them out, with authorities saying they would continue to enforce a regime of rationed access despite the even greater pace of arrivals from the other side in Greece.
"In this Europe, animals are sleeping in beds and we sleep in the rain," said 23-year-old Syrian woman Fatima Hamido on entering Macedonia. "I was freezing for four days in the rain, with nothing to eat."
Thirty-two-year-old Saeed from Syria said of the blocked border: "We know this was not Macedonia and the Macedonian police. This was the European Union. Please tell Brussels we are coming, no matter what."
Migrants had been pouring across the border into Macedonia at a rate of some 2,000 per day, en route to Serbia then Hungary and Europe's Schengen zone. Some 50,000 arrived on Greek shores in July alone by boat from Turkey.
POOR RELATIONS WITH GREECE
The surge in numbers had overwhelmed Gevgelija, testing the patience of a conservative government that faces an election in April and has for years been thwarted in its efforts to join the European Union and NATO by a dispute with Greece over Macedonia's name.
The government lashed out at Greece, as an EU member, for letting the migrants through and in some cases aiding their passage by chartering ships to take them from inundated Greek islands to the mainland.
On Friday, riot police fired tear gas and stun grenades to drive back angry crowds, in the latest flare-up in a migration crisis that has brought ripples from the conflicts of the Middle East to Europe's shores.
Some 600 were allowed through overnight, squeezing onto a dawn train north to the Serbian border. But more kept arriving on the Greek side, converging on a filthy, chaotic strip of frontier with little sign of an organised aid effort.
Some Greeks sold sandwiches and drinks to those prepared to pay. A man with a generator charged 1.5 euros to charge mobile phones.
Tired, angry and wet, one part of the crowd pushed through police lines, while others ran through open fields several kilometres from the bulk of police. Some small children were separated from their parents; people collapsed or staggered across with bloodied faces.
For many Macedonians, the crisis has echoes of 1999, when hundreds of thousands of ethnic Albanians took shelter in refugee camps on Macedonia's northern border during a war in neighbouring Kosovo, then a province of Serbia. (Additional reporting by Yannis Behrakis and Fedja Grulovic in IDOMENI, Greece; Writing by Matt Robinson; Editing by Raissa Kasolowsky and Dominic Evans)
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