German lawmakers launched a debate on Wednesday on legislative changes that would make it easier to deport asylum seekers convicted of crimes, spurred to action by public outrage over assaults on New Year's Eve in Cologne linked to foreign nationals.

Authorities say 561 police complaints - about 45 per cent of them related to sexual violence - have been filed in the wake of the attacks in the western German city, where groups of mainly North Africans encircled, sexually assaulted and robbed women near the main train station.

Lawmakers will discuss the proposals in the afternoon. Though the crackdown was prompted by the Cologne attacks, many of the crimes committed that night would not result in deportation under the new rules.

The legislative changes have to be approved by the Bundestag and Chancellor Angela Merkel's cabinet.

Deporting convicted asylum seekers is difficult in Germany because the risks they would face in their country of origin is often considered greater than the gravity of the crime.

If the proposed changes go into effect, asylum seekers will be deported even in the case of a suspended sentence for crimes such as bodily harm, homicide, rape, sexual assault and serial larceny.

A sentence of more than one year would further increase the chances of deportation, Interior Minister Thomas de Maiziere and Justice Minister Heiko Maas said as they presented the proposals on Tuesday.

"There will certainly be more deportations as a result of legislative changes because we are lowering the requirements for a deportation," Maas told public broadcaster ARD.

The government is also seeking changes to existing laws on sexual assault, which it has been working on since last year, months before the attacks in Cologne and other cities.

The changes seek to ensure that victims who do not resist assault - for fear of greater physical harm if they do - are better protected.

A special parliamentary committee discussed the New Year's Eve assaults early on Wednesday, and heard from Ralf Jaeger, the interior minister of North Rhine Westphalia state, where Cologne is based.

The debate has increased tensions over the influx of migrants and refugees in Germany. Some 1.1 million migrants entered the country in 2015 and several thousand people are crossing its southern border each day.

Federal states are "obligated" to deport the estimated 1,000 people whose asylum applications are being rejected each day, Peter Tauber, secretary general of Merkel's Christian Democrats (CDU), told regional newspaper Rheinische Post on Wednesday.

Though the number of deportations - mostly of migrants fleeing poverty rather than war - rose to over 18,000 in 2015, it remains far below the 1,000 asylum applications that are being rejected each day.

The migrant influx has placed an unprecedented burden on Germany's public administration, which is lagging behind on the screening of 476,649 asylum applications filed in 2015.

Another senior CDU politician, Michael Grosse-Bromer, said that Morocco, Tunisia and Algeria should be classified as safe third countries alongside several Balkan states in order to further ease deportation.

Voices from the centre-left were striking a similar tone on Wednesday, with Social Democrat lawmaker Burkhard Lischka arguing that the deportation of Algerians and Moroccans should be sped up considering their limited chances of being granted political asylum.