BRUSSELS - In a bid to slow a torrent of migrants and refugees, Germany and other nations instituted border controls Monday, while Hungary moved to reinforce its own porous frontier a day ahead of a planned crackdown on migration.
The measures along the path most favored by asylum seekers took hold before European Union interior ministers were set discuss a plan to resettle 160,000 asylum seekers across Europe.
But the proposal to parcel them out among 22 nations has sustained heavy criticism from Central and Eastern European countries, which oppose any measure that would require them to take in refugees.
In clear signs the route through Europe was tightening, border checks were imposed by Germany, Austria and Slovakia — a sharp reversal of the policies of open frontier that has become one of the hallmarks of E.U. integration. The Czech Republic boosted security forces at the border with Austria, but have not yet reintroduced border checks.
Highway traffic from Austria to Germany backed up for miles, while Austrian authorities deployed their army to aid overwhelmed relief efforts to deal with the exodus from countries such war-scarred Syria and Iraq.
Even Germany, which has declared that there are few limits to the number of asylum seekers it can accommodate, is increasingly under strain, with fresh records of new arrivals set nearly every day.
‘‘If Germany imposes border controls, Austria also has to do that,’’ Austrian Vice Chancellor Reinhold Mitterlehner said in Vienna. The new border measures are ‘‘a clear message to those concerned that uncontrolled crossing over the border can no longer take place,’’ he said.
On a main highway between Austria and Germany, traffic between the two nations had been blocked down to one lane, and German police were checking each car that entered, said Andreas Guske, a spokesman for the German police department of South Upper Bavaria.
Austrians have anxiously watched the flow of refugees pass through their country, generally relieved that their ultimate destination is Germany and the Scandinavian countries.
Trains from Vienna and Salzburg on Monday began to run again into Germany, after a brief interruption on Sunday, but travelers on the trains said that German authorities were stopping the trains and checking passengers’ documents onboard.
On Sunday, some 10,000 refugees crossed from Hungary into Austria, according to Austrian officials and refugee assistance groups. More than 7,000 were expected to arrive on Monday, they said.
An Austrian security official who is working on the refugee crisis said in an interview that Austria suspected that Germany may have introduced border checks to pressure Austria and other neighboring countries to commit to higher refugee quotas.
Germany has taken in by far the highest number of asylum seekers in Europe, and authorities said Monday that they could total 1 million people this year alone, up 200,000 from previous expectations.
In announcing the higher figure, German Vice Chancellor Sigmar Gabriel called for a ‘‘common European effort’’ to address the crisis. He made his comments in a letter addressed to members of his Social Democratic Party.
The Hungarian police said that more than 5,800 asylum seekers had entered their borders on Sunday, a number that significantly exceeded previous tallies.
New laws that come into effect on Tuesday criminalize unauthorized passage over the border. Refugee agencies are bracing for Hungarian authorities to significantly escalate their efforts to seal the border and sent all new asylum seekers into processing camps from which they could be deported if their claims are denied.
The border moves have had a cascade effect across Europe, as a succession of neighboring countries impose controls to keep migrants from streaming down the path of least resistance.
And only last week, Denmark temporarily closed a highway and suspended trains on its southern border with Germany, and French authorities have searched for migrants on trains crossing from Italy.
As Europe grappled with its response to the crisis, British Prime Minister David Cameron helicoptered into a Lebanese refugee camp run by the U.N. refugee agency near the Syrian border. The visit, which was conducted under heavy security, was the most high-profile move to date in his bid to shift the conversation away from resettling Syrians in Europe and toward helping refugees who remain in the region.
Britain has accepted only a small number of Syrians displaced by war, and has declined to participate in any E.U. quota system. But Cameron has argued that providing aid to refugees in Turkey, Jordan and Lebanon is a more effective way to deal with the crisis, and has trumpeted the fact that his country provides more assistance to refugees in the Middle East than any other European nation.
‘‘Without our investment in international development the numbers of people seeking to embark on a perilous journey to Europe would be far greater,’’ he said.
The death toll, meanwhile, continued to climb. Off a Greek island on Sunday, 34 refugees, including four infants and 11 boys and girls, drowned when their wooden boat overturned and sank. It appeared to mark the worst loss of life in those waters since the migrant crisis began.
Berlin says the emergency on its southeastern border is a question of national security. Germany has thus far stepped in to take in the most asylum seekers of any European Union nation, but its ability to aid refugees is being tested amid a record surge of 40,000 migrants over the weekend — from Syria, Iraq, Afghanistan and Pakistan, among other countries. Officials in the overwhelmed state of Bavaria, for instance, declared they have run out of space to house refugees.
Indeed, the move highlighted the backlash brewing against the open-arms policy on asylum seekers taken by Chancellor Angela Merkel. Within her ruling coalition, many are still smarting over her recent decision to allow in tens of thousands of refugees stranded in Hungary.
As Germany struggles to cope — turning army barracks, schools and former hardware stores into impromptu shelters — some politicians have called Merkel’s decision into serious question, arguing that the nation cannot provide sanctuary to all.
On Sunday, Bavarian Interior Minister Joachim Herrmann said at a news conference in Munich that cars would be monitored at the border in order to capture human traffickers and allow refugees to request asylum upon being stopped. But he said those who had already applied for asylum elsewhere in the E.U. — for instance, in Hungary or Austria — would be sent back to those countries in accordance with European laws.
‘‘Unchecked immigration on the scale of the past days constitutes a serious threat for the public safety and order in Germany,’’ said Herrmann, a member of the Christian Social Union, sister party of Merkel’s Christian Democratic Union.
The 28-nation E.U. is deeply divided over a plan backed by Germany and France to issue new migrant quotas to all nations. German leaders have said their country cannot shoulder the burden alone.
Faiola reported from Berlin, and Samuels reported from Budapest. William Booth and Souad Mekhennet in Vienna, Stephanie Kirchner in Berlin and Griff Witte in London contributed to this report