Austrian police are searching for at least one suspect after a multiple gun attack in the capital, Vienna, that killed four people.

Seventeen other people were wounded - some seriously - after gunmen opened fire at six different locations in the city centre on Monday evening.

One attacker was shot dead by police, officials said.

Interior Minister Karl Nehammer described the assailant killed by police as an "Islamist terrorist".

Two of those who died in the shooting were women and two were men. One of the women was reportedly a waitress. The second woman died of her wounds in hospital overnight, reports said.

The victims were in a city centre area busy with people in bars and restaurants, near Vienna's central synagogue, but it is not yet clear if that was the target.

Mr Nehammer advised people to stay away from the centre, as police cordoned off some streets and brought in reinforcements. Parents were told to keep their children home on Tuesday if they could.

Seven of the wounded have life-threatening injuries, Austrian media report.

Addressing a news conference, Mr Nehammer described the heavily armed gunman killed by police as an Islamic State (IS) sympathiser. His home had been searched and video material seized, the minister said. He had been wearing a fake explosive belt, police tweeted.

Earlier, Mr Nehammer said at least one "heavily armed and dangerous" attacker was believed to be still at large. Officials were quoted as saying there could have been as many as four attackers.

Austrian Chancellor Sebastian Kurz called it a "repulsive terror attack". The government called it "an attack on freedom and democracy".

The attack came hours before Austria imposed new national restrictions to try to stem rising cases of coronavirus. Many people were enjoying drinks and eating out before a midnight curfew.

The government has announced three days of national mourning, starting immediately, with flags to fly at half-mast and a minute's silence at midday. Schools will also have a minute's silence for the victims on Wednesday morning.

European leaders strongly condemned the shooting. British Prime Minister Boris Johnson said he was "deeply shocked by the terrible attacks".

The Vienna shooting comes after a spate of Islamist attacks in France.
What do we know about the attack?

Police say the incident began at about 20:00 (19:00 GMT), near the Seitenstettengasse synagogue, when a heavily armed man opened fire on people outside cafes and restaurants.

Members of the special forces quickly arrived at the scene. One policeman was shot and critically wounded before the perpetrator, armed with an automatic rifle, a pistol and a machete, was, in the chief's words, "neutralised" at 20:09.

Jewish community leader Oskar Deutsch said that the synagogue was closed at the time the attack began.

Footage posted on social media showed scenes of chaos as people ran through the streets with gunshots ringing out in the background.

Witness Chris Zhao was in a nearby restaurant when the shooting started.

He told the BBC: "We heard noises that sounded like firecrackers. We heard about 20 to 30 and we thought that to be actually gunfire. We saw the ambulances... lining up. There were victims. Sadly, we also saw a body lying down the street next to us."

A major anti-terrorist operation swung into action and police set up roadblocks around the city centre. Members of the public were told to stay away from the area and not to use public transport.

Police in the neighbouring Czech Republic said they were carrying out random checks on the border with Austria in case the gunman fled in that direction.
What reaction has there been?

In a post on Twitter, the Austrian chancellor said "we are experiencing difficult hours in our republic".

"Our police will act decisively against the perpetrators of this hideous terrorist attack. We will never allow ourselves to be intimidated by terrorism," he said. He was due to speak publicly after a cabinet video conference on Tuesday morning.

Austria had until now been spared the sort of attacks that have hit other European countries. Leaders across the region were quick to condemn the shootings, with French President Emmanuel Macron saying that Europe must not "give up" in the face of attacks.

"We, the French people, share the shock and grief of the Austrian people, struck this evening by an attack in the heart of their capital, Vienna. This is our Europe. Our enemies must know who they are dealing with," he said.

Three people died in a knife attack in a church in the French city of Nice last week in what Mr Macron said was an "Islamist terrorist attack".

The UK prime minister also said the country's "thoughts are with the people of Austria - we stand united with you against terror" while Home Secretary Priti Patel said "we stand ready to support in any way we can".

US President Donald Trump - on the campaign trail ahead of Tuesday's election - described it as "yet another vile act of terrorism in Europe".

"These evil attacks against innocent people must stop. The US stands with Austria, France, and all of Europe in the fight against terrorists," he tweeted.

His Democratic challenger Joe Biden condemned the "horrific terrorist attack", adding: "We must all stand united against hate and violence."

European Council President Charles Michel called it a cowardly act that violated life and human values.

Dutch Prime Minister Mark Rutte called the shooting "a heinous act" and expressed "solidarity" with Austria.