Calls for the segregation of refugees along religious and ethnic lines are surfacing in Germany as police increasingly grapple with violence among asylum seekers living in overcrowded transit camps.

Spokesman Ruediger Holecek of the 180,000-strong GDP police trade union said on Wednesday that conflicts in refugee shelters have risen in the past two months.

More than 200,000 migrants arrived in Germany in September alone - about the same for the whole of last year, after Chancellor Angela Merkel's bold open-door policy triggered an influx of asylum seekers from the Middle East, Africa and eastern Europe.

Germany's tolerant asylum laws and generous welfare benefits are a magnet. Its top-selling daily, Bild, citing a confidential document, reported on Monday that government estimates of arrivals this year have been raised to 1.5 million from 800,000 earlier.

"The conflicts normally start with the most trivial thing," Mr Holecek said. "The Muslims complain that the Christians have used the toilet and therefore do not want to go there, or that they do not want to use the kitchen because the Christians have cooked pork over there."

GDP deputy head Joerg Radek told Die Welt daily last week that police had reached their breaking point and stressed the need to prevent further clashes. "Segregation in accommodation facilities based also on religion is something I consider as absolutely reasonable."

Mr Radek also told Badische Zeitung newspaper that the lack of temporary housing is the main problem. "But accommodation based on religion and ethnicity would be the first solution," he said, echoing comments made by former interior minister Hans-Peter Friedrich.

Mr Friedrich told Welt am Sonntag newspaper on Sept 27 that it is "sad, that accommodation of refugees based on country of origin is apparently needed".

The segregation views have stirred controversy. Some politicians said it contradicted efforts to integrate the migrants.

Mr Rainer Wendt, head of the smaller DPoIG police trade union is against these views, saying implementation is difficult. On Wednesday, he told N.TV that violence in refugee camps has been happening for "months now and figures are exploding".

It is not just due to overcrowding. The "violent clashes that are ethnically or religiously motivated" occur "nearly daily", are "very deliberate and well thought out", he said, noting that rival ethnic groups want to gain supremacy.

Ms Hildegund Niebch, head of the refugee integration charity Diakonie in Hesse, said: "The conflicts are there because many people are pressed together under one roof."

Local officials - already having a tough time providing shelters in sport halls, school gymnasiums, fair and trade grounds, barracks and containers - are looking for more buildings to transfer refugees into as winter approaches.

In many camps it is common to see pictures of cots side by side. In some shelters, access to shower rooms and toilets is not separated, according to the media. There are also no separate rooms.

The only state which provides segregated housing based on country of origin is Thuringia, where a scuffle in Suhl in August ended with injuries to three policemen and at least 10 asylum seekers. The fracas was between Muslims and supporters of a man who tore pages from a Quran and flushed them down a toilet.

The Suhl incident was one of four major incidents recently. In Dresden, about 100 refugees from Syria and Afghanistan clashed, armed with cobblestones, plastic chairs, camping tables and tent poles.

In Bonn, police had to fire shots in the air to end a brawl.

On Sept 27, three policemen and 11 refugees were injured in Calden. It began when an Albanian slapped a Pakistani's face at lunchtime in a canteen.

Social workers said the German Cabinet's plans to keep refugees in transit homes for a longer duration could trigger more conflicts.

The potential for aggressive behaviour grows when asylum seekers fail to get official refugee status and have to be deported.

The BPtK Psychotherapists Association said about half of the more than 200,000 asylum seekers in Germany last year were "mentally sick".

About 40 per cent of asylum seekers in Germany are suffering from post-traumatic stress disorder, it said.

"Refugees who are suffering from psychological illness will have significant difficulties integrating into society," BPtK noted.