A series of violent incidents over the weekend in Germany has fuelled the nation's already charged atmosphere following terrorist attacks in France, Belgium, Turkey and Afghanistan.

The weekend began with Friday's shooting atrocity in a McDonald's restaurant and nearby Munich shopping centre, in which 10 people died, including the gunman, an 18-year-old Iranian–German named David Ali Sonboly.

When Sonboly opened fire on teenage shoppers and restaurant diners, police were still working to establish all the details in last week's axe-and-knife attack on a Bavarian train by a young Afghan refugee.

On Sunday evening local time, a woman was killed and two other people injured in the south-western city of Reutlingen, after they were attacked by a 21-year-old Syrian asylum seeker wielding a machete.

In another incident on Saturday, panic broke out on a regional train in the country's north when a 22-old-year man, apparently German, threatened passengers with a knife.

Police said he was suffering psychological problems and was drunk.

And in the past few hours, a reportedly deliberate explosion at a restaurant in Ansbach, Bavaria, has killed one person and injured eleven others.

German police on guard after the shooting rampage in Munich which left 10 dead. ( ABC News: Wayne Mcallister )

Asylum seeker crisis back in the headlines after attacks

Despite the different backgrounds to these incidents, they underline the political risks for Chancellor Angela Merkel after she opened Germany's borders last September to allow in refugees fleeing wars in Africa and the Middle East.

Up until a week ago, the asylum seeker crisis had largely disappeared from the headlines following the remarkably smooth resettlement of one million refugees who arrived in the country last year.

The last time the nation's refugee community was in the media was during the recent European football championships, when they were decked out in the German colours cheering on the country's footballers.

Berlin police keep a watchful eye on an anti-Islam protest over the weekend. ( Supplied: Andrew McCathie )

But the new right-wing nationalist party, the Alternative for Germany (AfD), has already moved to capitalise on the spate of attacks, by blaming Ms Merkel and her liberal refugee stance.

"If we were in power, this would not happen," the local AfD branch in Reutlingen declared in a tweet that was later deleted, after the attack in that city.

Police now believe the woman's murder was motivated by personal rather than ideological reasons.

Under its constitution, Germany must provide refuge for anyone escaping war and persecution.

This is not the first time that a mass shooting or acts of public violence have thrown the normally ordered world of Germany off course.

There have been eight since 2002.

But the scale of the Munich attacks, where authorities placed the Bavarian capital on full alert, has been extremely rare since World War II.

There have been calls to tighten Germany's gun laws in the wake of Sonboly's rampage, which happened just near Munich's Olympic stadium — the site where 11 Israeli athletes were held hostage and killed, along with a German police officer, by the Palestinian group Black September in 1972.

Authorities are now trying to answer key questions surrounding Sonboly's Friday night rampage, but have ruled out any link with the so-called Islamic State group.

Sonboly, who had a history of mental illness, had planned his attack for more than a year.

Authorities believe he was inspired by other mass shootings, including the far-right terrorist Anders Behring Breivik, whose act of savagery in Norway five years ago left 77 people dead.

German intelligence authorities say they have recently thwarted 10 terrorist attacks.

Still, there is a sense the nation has been remarkably lucky, despite a number of Islamic State fighters coming from Germany, and Berlin joining the international military campaign against the group.

Crowds gather in Munich to mourn the victims of Friday's attack. ( ABC: Wayne McAllister )

Poll finds 77 per cent of Germans fear future attacks

A poll after Monday's axe-and-knife attack on the Bavarian train showed a sharp rise in Germans' fears about their nation being a terrorist target.

Police believe that attacker had been spurred to act by Islamic State propaganda.

The poll, conducted by state broadcaster ZDF, found that 77 per cent of Germans believed their country would face terrorist attacks in the near future.

Two weeks ago, the figure stood at 69 per cent.

The assaults on the Bavarian train came just days after a truck driver — who Islamic State also claimed as one of its soldiers — ploughed into the crowd celebrating France's national day in Nice, killing 84 people, including two Berlin school students and their teacher.

The Nice attack seemed particularly shocking as it appeared French and Belgian authorities had broken up the terrorist cells responsible for the recent outrages in their respective nations.

In fact, France had been moving to end its state of emergency.

But Germany's Interior Minister, Thomas de Maiziere, has again warned: "Unfortunately, it is still not possible to provide a guarantee to prevent attacks always and everywhere."