BERLIN - A food queue fight in an overcrowded German refugee centre this week escalated into a mass brawl pitting 70 Pakistanis against 300 Albanians, fighting with fists, sticks and pepper spray.
By the time it ended, 14 people were injured, including three of the 50 police called in to contain the riot in a former airport building housing 1,500 asylum-seekers from 20 nations near the central city of Kassel.
Such disturbances have been rare, considering that Germany has taken in around half a million asylum-seekers this year and put them up in flats, army barracks, sports halls and tent cities.
Nonetheless, the mayhem Sunday served as a warning of how tensions can escalate between often traumatised people from different cultures sharing densely packed spaces as they battle tedium and uncertainty.
There has been trouble before. Six weeks ago a 25-year-old refugee started a riot when he ripped pages from a Koran and threw them into a toilet in a centre in Suhl, central Germany, according to police.
The ensuing violence left six police and 11 refugees injured. Police this week, after viewing video footage of the altercation, arrested 15 suspects on charges including attempted manslaughter.
Germany's police union Tuesday called for refugees to be separated by religion - especially between Christians and Muslims - and by country of origin, to minimise the potential for conflict.
Groups banding together by ethnicity, creed or clan were "attacking each other with knives and homemade weapons," said union chief Rainer Wendt, calling for special protection for Christians, women and minors.
Critics argued segregating migrants sends the wrong signal as Germany seeks to integrate them into a pluralistic society, and that portraying refugee centres as powder kegs fed the arguments of far-right agitators.
Islamic Studies expert Lamya Kaddor said mediators could help defuse simmering conflicts and rejected the idea that an "explosive mix" had been brewing as the "populist chatter" of xenophobes.
Most mainstream politicians agreed with her, and Interior Minister Thomas de Maiziere later shot down the segregation idea as "almost impossible right now in practical terms".
One of Germany's new refugee centres is the former town hall of Berlin's Wilmersdorf district, an ivy covered Nazi-era building that houses 850 refugees, most of them men from war-torn Syria, Iraq and Afghanistan.
Burly security guards stood outside this week, checking the IDs of anyone walking in or out, next to a sign reading "no photography".
"People really don't want to be photographed," said the camp's deputy director Gerd Schickerling of the charity Workers' Samaritan Federation.
"They may have fled the Islamic State and fear those people are watching them in Berlin too." In the courtyard, laundry hung from the windows of offices-turned-bedrooms, children played football and men stood idly, smoking cigarettes and killing time.
In the foyer, dozens crowded a stand of the city's migrant office seeking, with the help of Arabic translators, health service cards, monthly cash payments, political asylum, residency and work permits.
Looking on from a distance, dejected, stood three Africans, who said they had waited for weeks in vain as Syrian refugees got fast-tracked.
"African people, no. No paper, nothing - only eat, sleep, everyday stress," said Bamba Jaiteh, 19, of Guinea Bissau, in halting English.
"Arab people, Syria people - one week, two weeks, their papers are finished. African people, no. I don't know why," he added, straining to contain his frustration.
'Damned to wait'
The camp is run by about a dozen charity staff and 1,700 volunteers who rotate shifts to distribute donations, run medical and counselling services and teach literacy and German.
But despite their remarkable effort, other migrants too said they were frustrated.
"It's crowded, the food is no good, I want to leave," said Mohammed Uzer, 15, who told AFP he fled Pakistan after the Taliban killed his father.
"You don't know who'll come into your room. My friend lost his mobile phone, his clothes and 100 euros ($112). And there's a Syrian, not a good guy, who's always fighting, with words. I don't understand, he speaks Arabic." Dr Jessica Karagoel of immigration consultancy FaZIT said tensions tend to worsen with "crowded conditions, lack of privacy and the fact people from different countries often can't communicate".
A study by her centre had found that "conflicts are more likely where many people have to share one bathroom or one shower".
"The extra stress comes from having to wait in a foreign country, with little influence over the process, a loss of control, no idea about how long it will take and what the outcome will be." Schickerling said that "considering what they're up against, being 'damned to wait', I take my hat off to these people for staying so peaceful".
He said his centre had seen no violence at all, and that he saw no need for segregation.
"Germany is open to all religions, and that's something we need to share and live," he said. "We want to show that we're all in the same boat."