German Chancellor Angela Merkel promised to respond decisively to assaults on women in Cologne on New Year's Eve, which have stoked a fierce debate about her refugee policies after police said the attackers appeared to be of foreign origin. 

Some 121 women are reported to have been robbed, threatened or sexually molested there by gangs of mostly drunk men between 18 and 35 years old while out celebrating. 

Police say they have identified 16 suspects. Cologne's police chief, under pressure for the force's handling of the event, has said the perpetrators appeared to be of "Arab or North African" origin. 

German magazine Focus and newspaper Die Welt said police had found registration papers on some of the suspects, suggesting they had only recently arrived in the country. But authorities have not confirmed that.

Germany Sex Assaults

In this Dec. 31, 2015 picture, a group of men are seen at the Cologne, Germany, main station. (Markus Boehm/dpa via AP)

Merkel, whose support slipped last year when she resisted pressure to impose caps on refugees, insisting Germany could cope with the 1.1 million migrants who arrived in 2015, said the events were "completely unacceptable" and "intolerable." 

"There are some very serious questions, which arise from what has happened which have relevance beyond Cologne," she said, including establishing whether there are common patterns of behaviour by some groups of people who do not respect women.

'Cultural co-existence'

She said she would consider changing the law, boosting police numbers and making sure the deportation system was effective.

Asylum-seekers could be deported if they're found to have participated in a string of New Year sexual assaults in Cologne, Germany's justice minister said earlier on Thursday.

Officials have cautioned it's important not to cast suspicion on refugees in general. Still, Justice Minister Heiko Maas said in an interview with the Funke newspaper group that "deportations would certainly be conceivable."

Merkel said that "cultural co-existence" must be continually discussed. "We have a duty to give the right answers," she said.

Heiko Maas

German Justice Minister Heiko Maas made his comments about deportation being a possibility for those convicted in the New Year's incident to the Funke newspaper group. (Britta Pedersen/EPA)

Germans have been shocked by the attacks, which are reported to have taken place on a smaller scale in other cities including Hamburg. A poll for broadcaster ARD showed that 30 per cent of those surveyed said they would avoid big crowds because of the events in Cologne.

Similar events may have taken place in other countries. Finnish police say they received information that assaults had been planned on women at new year. In Switzerland, about six women have reported being sexually molested and robbed during New Year's Eve celebrations in Zurich after being surrounded by groups of men.

The ARD poll also showed 57 per cent of those asked wanted to bring back border controls, up 12 points from September.

Right-wing parties in Germany, including the Alternative for Germany (AfD), have jumped on the events to renew calls for a limit on the number of refugees allowed into Germany and for Merkel to close the country's border.

'Frau Merkel invited me here'

Top-selling daily Bild published excerpts of a report from a policeman on duty in Cologne on New Year's Eve, which was later confirmed as accurate by police.

One man is reported to have grinned as he ripped up his residency permit and told a policeman: "You can't do anything to me. I'll just pick up another one tomorrow."

Another is reported to have said: "I'm Syrian. You need to be nice to me. Frau Merkel invited me here."

German weekly Die Zeit contrasted the violence in Cologne with the feel-good scenes in Munich four months ago when locals greeted arriving refugees with cheers, food and blankets.

Even if there was no proof the attackers were recent arrivals, the newspaper said that what happened seemed to confirm the fears of some Germans that young men were coming into the country who were violent, disdainful of women and prepared to ignore German laws.

"Cologne is a tipping point. Policy towards refugees must not be reinvented because of these assaults. But can only be sold successfully if the rule of law is defended with determination," the paper wrote.