The shooting, which has been referred to as a terrorist attack by Austrian Chancellor Sebastian Kurz, took place in downtown Vienna just hours before the reimposition of the nationwide lockdown, which has been called to stem the spread of Covid-19.

In a latest update, Vienna Police said three deceased include two men and one woman.

Among the 15 injured, one was a Vienna police officer.

The assault was carried out by at least one suspect who was shot and killed by officers, police said.

Vienna Police is considering the attack to have an Islamist motive.

Addressing a press conference, Austrian Interior Minister Karl Nehammer said as quoted by CNN, "The radicalized person is someone who is an IS sympathizer."

Reacting to the shooting, Kurz tweeted, "We are currently going through difficult times in our republic. I would like to thank all the emergency services who risk their lives, especially today for our safety.

"Our police will take decisive action against the perpetrators of this hideous terrorist attack."

Australian Prime Minister Scott Morrison tweeted, "Deeply shocked by the awful terror attacks in Austria. The situation remains fluid and details of the attack are still not clear. I have contacted Austrian Chancellor Sebastian Kurz to convey our thoughts, condolences and assurances to the Austrian people."

"We pray for, and stand firm with, our Austrian friends against acts of violence, terror and intimidation, and all they seek to undermine."

US President Donald Trump tweeted, "Our prayers are with the people of Vienna after yet another vile act of terrorism in Europe. These evil attacks against innocent people must stop. The U.S. stands with Austria, France, and all of Europe in the fight against terrorists, including radical Islamic terrorists."

US Democratic nominee for Presidential election Joe Biden tweeted, "After tonight's horrific terrorist attack in Vienna, Austria, Jill and I are keeping the victims and their families in our prayers. We must all stand united against hate and violence."

Indian Prime Minister Narendra Modi said on the micro-blogging site, "Deeply shocked and saddened by the dastardly terror attacks in Vienna. India stands with Austria during this tragic time. My thoughts are with the victims and their families."