As if fear, hunger, thirst, worry and exhaustion were not enough to endure, new trials emerged Thursday for those on the 1,000 mile-plus trek into Europe: torrential rains and thick mud.

About 7,000 refugees and migrants, including many families lugging young children, braved relentless downpours Thursday to cross Greece's northern border into Macedonia in what Greek police said was the largest single wave they had seen so far.

At the northern village of Idomeni, crowds gathered before dawn, using anything they could find - plastic sheeting, garbage bags, hooded jackets, even a beach umbrella - in a futile attempt to stay dry. Sneakers stuck in the mud. Rain dripped off hoods and caps. All were soaked to the skin.

Parents held their children aloft in the rain, to make sure the Macedonian police would see them and let them through checkpoints. Other mud-splattered children dragged luggage and stumbled into rain-filled potholes, climbing out crying.

By early afternoon, all had crossed but thousands more were on their way, heading to the Greek mainland in ferries.

The surge came after Greek authorities managed to register about 17,000 people on the eastern island of Lesbos in just a few days, speeding their trip north. Greece's caretaker government chartered two extra ferries and sent additional registration staff to Lesbos to ease overcrowding on the Aegean island, where more than 20,000 refugees and migrants had been living in precarious conditions after arriving on dinghies from the nearby Turkish coast.

Greece, Italy and Hungary have been overwhelmed this year - and especially this summer - by a flood of refugees and migrants seeking safety in Europe. The vast majority of those arriving in Greece are Syrians fleeing their country's vicious civil war, followed by Afghans.

In Brussels, the 28-nation European Union is seeking backing for plans to distribute 200,000 people among its members, but is meeting fierce resistance from some nations. Most of those heading north hope to settle in wealthier EU nations like Germany or Sweden.

At Idomeni, about 4,000 stood in a muddy field early Thursday, waiting for Macedonian police to let them across. Thousands more sought shelter under tents pitched in fields or headed to the Idomeni train station, where they huddled around fires to stay warm. The train station's cafe was converted into a shelter for women and children, some of whom were running fevers.

Macedonian police formed a human chain on the border to limit the flow of refugees into more manageable groups, letting families with young children cross first. Occasionally they used batons and shields to push back migrants attempting to rush through ahead of their turn.

For some, the chaos, the cold and the rain were unbearable. One Iraqi man was asking anyone he could find how he could return home. He wanted to fly back to Iraq, he said, he couldn't bear the conditions any more to reach Europe.

Abas Jizi, a 30-year-old supermarket employee from Deir ez-Zor in Syria, huddled around a fire with his wife and three children at the Idomeni train station, cradling his 1-year-old son.

"I was hit by the police" in Lesbos, he said. "The situation was very bad. We waited for 10 days to get our papers. We got to Athens yesterday and we set off straight away for here."

He had no choice but to leave Syria, he said. "In my country the situation is very bad. The helicopters fly over the city and they bomb."

Jizi is aiming to get his family to Denmark. "I don't have anyone there but I believe I can rebuild my life."

Waseem Absi, a 30-year-old from Ariha in northern Syria, was aiming to reach the Netherlands and rejoin other family members there. He had heard of problems further up the route in Hungary, where the migrants have faced a hostile reception, but was undaunted.

"I'm not going to be afraid of anything," he said as he trudged through the mud with four friends, carrying an open tent to keep off the worst of the rain.

Absi reached Lesbos after spending 20 days in Turkey.

"The conditions were terrible, but there were more than 10,000 people. It wasn't the Greek police's fault, they couldn't do anything with such a crowd," he said.

He said he tried to bribe Greek police to get his registration papers faster, but no one would take the money. He did see other people hawking registration papers for $112 each.