Austrian police said on Tuesday they had identified a gunman who took part in a shooting rampage across Vienna that left four people dead as a Daesh terror group supporter.

As the country mourned the victims of the Monday night assault, security forces swooped on 15 different addresses looking for possible accomplices and seeking to determine if one or several shooters had been involved.

In a televised address on Tuesday, Austrian Chancellor Sebastian Kurz condemned a "repulsive terror attack" and said the deceased were "an older man, an older woman, a young passer-by and a waitress", Kurz said.

The suspected killer, who was shot dead by police, was named by Austrian authorities as 20-year-old Daesh sympathiser Kujtim Fejzulai, who had dual Austrian and Macedonian nationality.

He had been convicted of a terror offence in April last year for trying to travel to Syria, Interior Minister Karl Nehammer told the APA news agency, adding that at least one other arrest had been made in connection with the shooting spree.

A large swathe of central Vienna was cordoned off early on Tuesday afternoon around the location of the shootings, an area not far from the historic opera house that was teaming with people in bars and cafes on Monday night on the eve of a new national coronavirus lockdown.

The president of Vienna’s Jewish community Oskar Deutsch said shots had been fired "in the immediate vicinity” of the Stadttempel synagogue, but added that it was currently unknown whether the temple — closed at the time — had been the target.

Police officers could be seen combing the ground near the historic Schwedenplatz area looking for evidence on Tuesday.

Flags lowered 

Police say they are investigating the possibility that further assailants may still be at large, and several neighbouring countries have stepped up border checks.

"It’s difficult for us at the moment to define whether the attack was carried out by one perpetrator or more than one,” said Gerhard Puerstl of the Vienna police.

Austria had until now been spared the sort of major attacks that have hit other European countries, but Monday’s shooting followed a spate of extremist attacks in France.

It triggered an outpouring of solidarity from world leaders with French President President Emmanuel Macron said the French shared the "shock and sorrow” of the Austrian people.

Across the country, flags have been lowered to half mast on public buildings and people observed a minute of silence at noon (11:00 GMT) as church bells rang out in remembrance.

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

‘Sounded like firecrackers’ 

A total of 22 people were brought to Vienna hospitals over the course of the night with injuries from the attack, of whom eight were subsequently released.

Fourteen have serious injuries, with three in a "critical but stable” condition in intensive care, Vienna hospitals’ association spokesman Christoph Mierau told AFP.

Police said an officer was among the injured.

The first shots were heard at around 8 pm (1900 GMT).

"It sounded like firecrackers, then we realised it was shots,” said one witness quoted by public broadcaster ORF.

A gunman "shot wildly with an automatic weapon” before police arrived and opened fire, the witness added.

Another spoke of at least 50 shots being fired.

"The police came in and said, ‘you all have to stay inside because there’s a probably a dead man there’,” said waiter Jimmy Eroglu, 42, who heard shots as the attack unfolded near his restaurant.

Speaking to ORF, Kurz said the attack had been carried out with automatic weapons and had been "prepared professionally”.

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

Interior Minister Nehammer told a press conference earlier Tuesday that police had used explosives to blast their way into the apartment of the dead suspect who had been "heavily armed”.

Nehammer urged Vienna residents to remain in their homes and said children would not be expected to go to school on Tuesday.

Germany joined the Czech Republic in stepping up checks at their borders with Austria as Chancellor Angela Merkel said: "The fight against these assassins and those who instigate them is our common struggle.”

"After France, it is a friendly nation that has been attacked. This is our Europe. Our enemies must know who they’re dealing with. We will concede nothing,” Macron tweeted in both French and German.

France is still reeling from the killing of three people at a church in the Riviera city of Nice last Thursday and the beheading of a schoolteacher by a suspected Islamist outside Paris on October 16.

Leaders of other nations also voiced support for Austria.