Overwhelmed police on the Greek island of Kos on Tuesday beat migrants with truncheons and sprayed them with fire extinguishers as its mayor warned of a "bloodbath" if the crisis gets worse.
Amid mounting tensions across Europe over the spike in new arrivals, Germany's police union called for a scrapping of Europe's visa-free Schengen travel zone -- while Italian police said they had arrested nearly 900 suspected human traffickers since January 2014, but added that the kingpins were at large.
In Kos, the migrants, mostly Afghans and Syrians, were being relocated to a local football stadium after camping along roads and beaches for weeks.
Four police used truncheons and fire extinguishers seemingly to prevent a stampede as a crowd tried to squeeze through a door into the stadium, an AFP photographer at the scene said.
At least one woman had fainted in the heat and many children were crying as the tightly packed mass of people jostled for space, just days after the country's handling of migrants came under fire from the United Nations.
Tensions on the tourist island are high with its mayor claiming there were 7,000 migrants stranded on Kos, which has a population of only 30,000 people.
On Monday, a Kos police officer was suspended after being filmed slapping and shoving migrants queueing outside the local police station as they waited to be documented so they could go on to Athens.
Kos mayor Giorgos Kiritsis told the Greek news agency ANA there "was a risk of bloodshed if the situation degenerates".
A police source in Athens told AFP that the latest incident occurred because the migrants were trying to get into a police post to get their papers sorted, but the officers wanted to process them inside the stadium.
Greek Prime Minister Alexis Tsipras last week said the refugee crisis "surpasses" his crisis-hit nation's resources and called for European Union assistance.
The UN refugee agency's division for Europe said last week that 124,000 refugees and migrants have landed in Greece since the beginning of the year.
The agency said that Athens' response to the problem had so far been "totally shameful", with many of those landing on the eastern Aegean islands near Turkey forced to sleep in the open, lacking access to washing facilities and toilets.
In Germany, the police union meanwhile called for the reintroduction of internal European border controls and sought more personnel to deal with a record flood of refugees.
"From a policing point of view, a return to border controls would be the best of all measures," said Rainer Wendt, chairman of the German Police Union, in a newspaper interview.
In EU talks on the wider refugee crisis, "Germany should not take the threat of bringing back (border) controls off the table too readily," Wendt told the Passauer Neue Presse.
Europe has abolished passport controls within the so-called Schengen zone, which incorporates 22 EU members as well as Switzerland, Norway, Iceland and Liechtenstein.
However, police have stepped up spot-checks of travellers on inter-European trains, highways and flights.
In Italy -- which along with Greece is one of the countries worst affected by the refugee crisis -- police data showed that 888 suspected people traffickers had been arrested since January 2014 but the overwhelming majority were small-fry.
Of those arrested, the majority are from Egypt and Tunisia, data published in the Catholic daily Avvenire showed.
However, despite increased police cooperation between Italy and the countries concerned -- with the exception of war-torn Libya -- none of the internationally-sought after masterminds have been arrested, it said.
Avvenire highlighted the case of Ethiopian suspect Ermias Gharmiay, accused of having accumulated as much as $70 million (63.5 million euros) from chartering boats to smuggle people into Europe, including a vessel which capsized in 2013 off the coast of Lampedusa in Italy, leaving 366 dead.
Gharmiay is believed to operate from Libya, where the only threat to his empire comes from the armed militia's interest in the lucrative market, the daily said, citing police sources.