Multiple people have been killed in a gun attack at a high school in the southern Austrian city of Graz.

Police said 10 people were killed during the incident — including the suspected shooter — while several more people were seriously injured.

Another victim later succumbed to their injuries in hospital.

"The rampage at a school in Graz is a national tragedy that has deeply shaken our entire country," Austrian Chancellor Christian Stocker said.

"There are no words for the pain and grief that we all — all of Austria — are feeling right now."

A police operation began at 10 a.m. local time (0800 UTC), with authorities later saying the school had been successfully evacuated.

"The situation is secure," police said. "No further danger is expected."

Police said that a helicopter had been deployed as part of the operation.

Graz has around 300,000 inhabitants and is the capital of Styria state.

What do we know about the suspect?

Austrian authorities described the shooter as a 21-year-old man who was not known to police.

He carried out the school shooting with a long gun and a handgun that he owned legally.

Police said the suspected perpetrator's motive was initially unclear.

They said the gunman killed himself in a toilet in the school after carrying out the shooting.

Interior Minister Gerhard Karner said that the shooter was a former student at the high school who did not graduate.

He said on Tuesday afternoon that 10 people were killed in the attack, including the suspected perpetrator. Among them, six of the victims were female and three were male.

The minister added that 12 people were wounded in the shooting, with some of them sustaining serious injuries. One of the wounded individuals later died in hospital, local medical authorities said.

Austrian public broadcaster ORF reported that both students and teachers were among the casualties.

Police said they believed that the shooter had acted alone.

Austria declares 3 days' mourning

Austria's chancellor declared three days of national mourning following the shooting, which he described as a "dark day in the history of our country."

Flags are to be flown at half-mast, with national minute of mourning scheduled for 10 a.m. on Wednesday.

President Alexander van der Bellen said that the attack had hit Austria "right in the heart."

"Austria is in mourning," he said. "And in this hour, we are standing together."

European leaders express condolences

The chancellor of neighboring Germany, Friedrich Merz, said Germans were mourning with Austrians.

"Horrific news from Graz. Our thoughts are with our Austrian friends and we mourn with them," he said.

European Commission President Ursula von der Leyen also expressed her condolences in an X post.

"My thoughts are with the victims, their families and friends," she said. "Schools are a symbol for youth, hope and the future. It is hard to bear when schools become places of death and violence."

EU top diplomat Kaja Kallas said she was "deeply shocked by the news of the school shooting in Austria."

"Every child should feel safe at school and be able to learn free from fear and violence."

How strict are Austria's gun laws?

Austria has nearly 30 civilian firearms per 100 people, according to the Small Arms Survey research project.

The Alpine country has banned automatic weapons and pump action guns, while revolvers, pistols and semi-automatic weapons are allowed with a permit.

Rifles and shotguns are permitted with a firearms license, a valid hunting licence or for members of shooting clubs.

In 2020, four were killed and 22 injured in a shooting in the center of Vienna. That attack was carried out by a sympathizer of the so-called Islamic State (IS) group.

Tuesday's school shooting appeared to be the deadliest attack in Austria's post-World War II history.

Edited by: Kieran Burke and Zac Crellin