Several suspected perpetrators of what the Austrian government is calling a terror attack in Vienna are on the loose and a manhunt is underway, Interior Minister Karl Nehammer said on Monday, calling the attackers "heavily armed and dangerous."

"We have brought several special forces units together that are now searching for the presumed terrorists. I am therefore not limiting it to an area of Vienna because these are mobile perpetrators," Nehammer told broadcaster ORF, urging the public to stay indoors until the all-clear is given.

Reports say the attack unfolded across several crime scenes in the vicinity of a major synagogue in Vienna, with multiple injuries, some severe, and potentially multiple deaths.