German police said Sunday a man arrested for a knife attack on a pro-refugee politician was deemed mentally fit to face justice, had voiced "xenophobic sentiments" and had a history of far-right activism.

The 44-year-old man slashed the neck of a mayoral candidate in the western city of Cologne on Saturday and wounded four others in a crime that shocked Germany as it grapples with a record migrant influx.

The candidate, Henriette Reker, 58 – an independent close to the ruling Christian Democrats (CDU) of Chancellor Angela Merkel – suffered serious wounds but was in a stable condition Sunday.

An initial psychological assessment of the unemployed suspect found "no evidence to diminish his criminal responsibility", said police and prosecutors in a joint statement.

He would face a custodial judge later on Sunday on one charge of attempted murder and four counts of causing grievous bodily harm.

After his arrest at the scene, police said the suspect had made statements that "suggested xenophobic sentiments".

"He said he had in the past been active in the rightwing scene, without giving further details," the statement said indicating that his involvement dated back to the 1990s.

Questions about the nature of his involvement and the "level of intensity" were part of the ongoing investigation, it said.

Despite the attack, voting was under way on Sunday for the mayorship of Cologne, Germany's fourth-largest city which has a population of 980,000.

Reker, who has coordinated city efforts to accommodate refugees, is seen as having a good chance of winning.

Hospital sources told local media she was expected to make a full recovery.

Increasing radicalistation

Security experts have warned of the threat of political violence due to rising tensions sparked by the record influx of refugees to Germany, which is expecting to register between 800,000 and one million asylum requests this year.

Domestic intelligence chief Hans-Georg Maassen warned in late September of a radicalisation of rightwing groups and "a greater willingness to use violence" by all extremist groups.

Police union chairman Rainer Wendt last week warned that security forces must keep a close eye on the resurgent anti-Islamic PEGIDA movement in eastern Germany and "prevent the spread of a new, organised right-wing terrorism".

The nationalist and anti-foreigner movement, whose full name is "Patriotic Europeans Against the Islamisation of the Occident", will on Monday mark one year since the first street rally of what started out as a xenophobic Facebook group in the eastern city of Dresden.

In 2011, Germany was shocked by the discovery of a neo-Nazi death squad calling itself the National Socialist Underground (NSU) which had killed 10 people, nine of them migrants.

"There must not be a second NSU," said Wendt.

(AFP)