As refugees from Syria and other war-torn nations make their way from Hungary to Germany and other western European destinations, thousands more are stuck in Greece and Macedonia, with no idea when they can move on.
The United Nations refugee agency said about 30,000 migrants have arrived in Greece, including 15,000 to 18,000 on the island of Lesbos alone, while 7,000 Syrian refugees have arrived in the former Yugoslav republic of Macedonia.
The migrants are waiting to be screened before they are allowed to head on to seek asylum.
Interim Interior Minister Yiannis Mouzalas was quoted by Agence France Presse, telling a local radio station that the situation on Lesbo is "on the verge of explosion."
Reuters news agency said the U.N. refugee agency has issued an emergency appeal stating that the number of refugees fleeing across the Mediterranean to Europe will reach 400,000 this year.
Melissa Fleming, a spokeswoman for the U.N. refugee agency, was quoted by Reuters as telling reporters in Geneva Tuesday that European nations must establish "a guaranteed relocation system" in which each country pledges to accept a predetermined number of migrants.
Peter Sutherland, U.N. Secretary-General Ban Ki-moon's special representative on migration, said it's "not enough" for countries like the United States and wealthy Persian Gulf states to give money to help Syrian refugees -- they must take them in, too.
Speaking to reporters in Geneva, Sutherland said Lebanon, Jordan and Turkey have taken in about 4 million Syrian refugees. “Buying your way out of this is not satisfactory,” he said Tuesday.
"Proximity doesn't count, capacity does count, and I do say that taking refugees is separate from giving money," he said.
Peter Boogaard, a spokesman for the National Security Council, said the United States is in contact with countries in the Middle East and Europe grappling with the influx of more than 340,000 people from the Middle East, Africa and Asia.
Billions in aid
The U.S. has provided over $4 billion in humanitarian assistance since the Syrian crisis began, and over $1 billion in assistance this year, Boogaard said.
The Obama administration said it is “actively considering” ways to be more responsive to the global migrant crisis, including refugee resettlement.
AFP reports it has learned the European Commission chief Jean-Claude Juncker is expected to unveil a plan Wednesday that would see Germany take in 31,000 migrants, France accept 24,000 and Spain another 15,000.
Germany's Deputy Chancellor Sigmar Gabriel told reporters Monday his country will be able to accept as many as 500,000 refugees a year for a few years.
Germany has previously said it expects to take in 800,000 refugees this year.
Meanwhile, Hungary Prime Minister Viktor Orban vowed Tuesday to speed up the construction of an anti-migrants fence on its southern border as it emerged that the defense minister had quit because of the slow pace.
Orban paid a snap visit to the border late Monday to check on progress, later telling the Magyar Idok online newspaper that he was convinced "the works in progress have to be sped up."
Hungarian police on Monday struggled to control refugees entering by the thousands at Hungary’s border with Serbia.
Police kept a large group of exhausted and anxious refugees in a holding area, a few meters from a gap in the border fence where a rail line linking Serbia and Hungary passes, and where most refugees have been entering on foot.
When buses arrived to begin loading the refugees to take them to a registration center, hundreds of them stampeded. Some tried to board the buses, while others set out on foot on the highway to Budapest, where many hope to catch trains to the Austrian border and on to Germany.
“Every day, thousands of people come across. Only today, it’s more than 2,000 people who have crossed this border line, which means they have entered the European Union,” said Kristof Gancs, a spokesman for Hungarian Interchurch Aid, a relief organization.
Gancs and other relief workers gave directions to the migrants arriving on foot along the railroad tracks, some pushing strollers with babies and elderly people in wheelchairs.
Some material for this report came from AP.
WATCH: Related video from Hungary-Serbia border by VOA's Luis Ramirez