"A police operation is currently underway... The reason for its deployment is that shots were heard in the building," police wrote in X, confirming the attack in Graz, AFP reported.
According to Austrian public broadcaster ORF, which cited police, a student was behind the shooting, which led to the evacuation of the school.
Police spokesman Fritz Grundnig said students and teachers were among several people seriously injured.
Attacks in public places are rare in the Alpine state with a population of almost 9.2 million.
In February, a knife attack in southern Austria killed a teenager and injured five others. A 23-year-old Syrian asylum seeker was detained. | BGNES