Austrian police have arrested 14 people in raids linked to Monday's deadly attack in Vienna and have found no evidence that a second shooter was involved, Interior Minister Karl Nehammer said on Tuesday.

“There have been 18 raids in Vienna and Lower Austria and 14 people have been detained,” Nehammer told a televised press conference.

The minister added that police believe that the attack in central Vienna that left five people dead was carried out by a lone gunman, Kujtim Fejzulai, a 20-year-old sympathiser of the militant Islamic State (IS) group who was killed by police on Monday night.

The video material evaluated by the police “does not at this time show any evidence of a second attacker,” Nehammer said.

Fejzulai, a dual Austrian and Macedonian national, was convicted of a terror offence in April last year for trying to travel to Syria.

Nehammer said he had been on a de-radicalisation programme and had managed to secure an early release.

“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 through this,” the minister said.

Earlier, hundreds of police fanned out across Vienna, searching for suspected perpetrators of the attack in the city’s centre, after what a government minister said was an “Islamist terrorist” incident.

In an early morning televised news conference, Nehammer repeated calls for the public to stay off the streets.

Nehammer said police had shot to death one attacker, a man wearing an explosives belt that turned out to be fake.

Police at the time said the attack, in six locations including near a synagogue in the centre of town, was carried out by “several suspects armed with rifles”.

They said three people had died, with public broadcaster ORF stating one of them was a passer-by.

Vienna mayor Michael Ludwig told ORF that 15 people had been taken to hospital, seven of them seriously wounded.

Broadcaster ORF later said a fourth civilian, a woman, had died.

Police stated earlier that an officer had also been hurt during the assaults.

The shooting began just hours before Austria was to re-impose a coronavirus lockdown, with people out in bars and restaurants enjoying a final night of relative freedom.

The attack started at around 8pm when the first gunshots were heard in the city's centrally located first district.

In a press conference earlier, Nehammer said: “According to what we currently know, there is at least one attacker who is still on the run.”

Speaking to ORF, Austrian leader Sebastian Kurz had said that the suspected attackers were “were very well equipped with automatic weapons” and had “prepared professionally”.

Earlier, he tweeted: “Our police will act decisively against the perpetrators of this repulsive terror attack,” adding that “we will never be intimidated by terrorism and we will fight this attack with all means”.

Kurz said that while police were concentrating on the anti-terror operation, the army would take over the security of major buildings in Vienna.

Nehammer urged Vienna residents to remain in their homes and keep away from all public places or public transport. He said that children would not be expected at school on Tuesday in Vienna.

Sirens and helicopters could be heard in the city centre as emergency services responded to the attack.

An AFP photographer said that large numbers of police were guarding an area near the city's world-famous opera house.

The location of the initial shooting was close to a major synagogue.

The president of Vienna's Jewish community Oskar Deutsch said that shots had been fired “in the immediate vicinity” of the Stadttempel synagogue, but added that it was currently unknown whether the temple itself had been the target of an attack.

He said that the synagogue and office buildings at the same address had been closed at the time of the attack.

'Cowardly act'

“It sounded like firecrackers, then we realised it was shots,” said one eyewitness quoted by ORF.

A shooter had “shot wildly with an automatic weapon” before police arrived and opened fire, the witness added.

Austria had until now been spared the sort of major attacks that have hit other European countries.

The Pakistan Foreign Office condemned the attack in the "strongest terms".

"We would like to convey our deepest condolences and heartfelt sympathies to the families of the innocent victims and wish speedy recovery to those injured," it said in a statement.

United States President Donald Trump said that "our prayers are with the people of Vienna after yet another vile act of terrorism in Europe", adding that these "evil attacks against innocent people must stop".

President Emmanuel Macron of France, which has experienced two serious attacks in recent weeks, tweeted that “we French share the shock and sorrow of the Austrian people”.

“After France, it's a friendly nation that has been attacked,” he added, referring to the killing on Thursday of three people by an attacker in the southern city of Nice and the beheading of a schoolteacher by a suspected Islamist outside Paris several days before.

EU Council chief Charles Michel tweeted that the bloc “strongly condemns this cowardly act”.

And Germany's foreign ministry tweeted that the reports from Austria were “horrifying and disturbing”.

“We can't give in to hatred that is aimed at dividing our societies,” the ministry added.

Czech police said they were conducting checks on the border with Austria.

“Police are carrying out random checks of vehicles and passengers on border crossings with Austria as a preventive measure in relation to the terror attack in Vienna,” Czech police tweeted.

Italian Prime Minister Giuseppe Conte also “strongly condemned” the shootings.

“There is no room for hatred and violence in our common European home,” he said on Twitter in Italian and German.

Additional reporting by Naveed Siddiqui.