Austrian investigators were on Tuesday piecing together the Monday evening rampage through central Vienna by a lone gunman and later claimed by the Islamic State (IS) group, as Chancellor Sebastian Kurz called for a European response to "political Islam".

Four people were killed when Kujtim Fejzulai, described as a 20-year-old IS sympathiser who had spent time in prison, opened fire with a Kalashnikov in a busy area of the Austrian capital the day before the country went into a new coronavirus lockdown.

IS -- which has claimed numerous attacks in Europe -- said Tuesday a "soldier of the caliphate" was responsible for the carnage, according to its propaganda agency.

Vienna terror attack
One of the gunmen was shot dead by police who said they were hunting for at least one more attacker still at large Photo: AFP / Joe Klamar

Police shot the gunman dead on Monday and later swooped on 18 different addresses and made 14 arrests as they looked for possible accomplices and sought to determine if he had acted alone.

After reviewing CCTV footage of the attack in an area teaming with bars and restaurants not far from the historic sights of central Vienna, Interior Minister Karl Nehammer said the video "does not at this time show any evidence of a second attacker".

Vienna police have asked people who filmed moment of the attack to share their recordings with the authorities to aid in tracking the gunman's route through the capital, rather than posting them to social media.

On Fejzulai's computer, investigators found incriminating evidence including a photograph recently posted on Facebook showing him carrying the automatic weapon and a machete used during the attack.

Police said he was also wearing a fake explosive belt.

Austrian Chancellor Sebastian Kurz condemned the shooting as a "repulsive terror attack", which he said killed a waitress, a young passer-by and an older man and woman.

He called on the European Union to fight against "political Islam" saying it was an ideology that represented a "danger" to the model of the European way of life, in an interview published in Germany's Die Welt newspaper.

His government will face questions about how an individual known to security forces had been able to buy weapons and cause havoc on the streets of the usually peaceful capital, often listed as having the world's highest quality of life.

Vienna terror attack
The shooting began just hours before Austria was to re-impose a coronavirus lockdown, with people out in bars, restaurants and at the opera, enjoying a final night of relative freedom Photo: AFP / Joe Klamar

The investigation is spanning several countries, with Switzerland making two arrests and Macedonia, where Fejzulai has family roots, cooperating with the Austrian authorities.

The attack came after several Islamist atrocities in France, including an assault on churchgoers in the Mediterranean city of Nice and the beheading of a schoolteacher near Paris.

The recent re-publication of cartoons of the Prophet Mohammed in France has caused new tensions worldwide, sparking protests in some Muslim-majority countries and calls from several terror groups for their followers to take revenge.

Britain on Tuesday upgraded its terrorism threat level from "substantial" to "severe".

Nehammer said Fejzulai had been convicted and jailed for a terror offence in April last year for trying to travel to Syria.

The dual Austrian and Macedonian national had then been admitted to a government-funded de-radicalisation programme and had managed to secure an early release in December from a 22-month prison sentence.

"The perpetrator managed to fool the de-radicalisation programme of the justice system, to fool the people in it, and to get an early release," Nehammer said.

"It was clear that the attacker, despite all the outward signs of having integrated into society, did exactly the opposite."

A large swathe of central Vienna was cordoned off around the location of the shootings as police combed the area.

"It sounded like firecrackers, then we realised it was shots," one witness told public broadcaster ORF after the attack began. Another spoke of at least 50 shots being fired.

The small Alpine nation of nine million people had until now been spared the sort of major attacks that have hit other European countries such as France, Germany and Britain in the last decade.

The last significant attacks date back to the 1970s and 1980s and were carried out by pro-Palestinian militants.

"This isn't Berlin and it isn't Paris. We're perhaps a big city but nothing really bad ever happens here," said hotel receptionist Sharut Gunduz.

The bloodshed triggered an outpouring of solidarity from world leaders with French President Emmanuel Macron saying the people of France shared the "shock and sorrow" of the Austrian people.

Across the country, flags were lowered to half mast on public buildings and people observed a minute of silence at noon as church bells rang out.

Kurz, President Alexander Van der Bellen and other officials took part in a wreath-laying ceremony in honour of the victims.

Twenty-three wounded people were in hospital Tuesday, with seven in a critical condition, Vienna's hospital association said.

Police said an officer was among those hurt.

"The fight against these assassins and those who instigate them is our common struggle," said Chancellor Angela Merkel.

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