Two suspected extremists have been arrested in Austria after it was discovered that one was planning to attack an event in Vienna in anticipation of upcoming concerts by Taylor Swift, Austrian authorities said.

The main suspect, who is 19 years old, was arrested in Ternitz, south of Vienna, and the second person in the Austrian capital.

Franz Ruf, the director of public security at Austria's interior ministry, said authorities were aware of "preparatory actions" for a possible attack.

Roof said the 19-year-old had pledged allegiance to the Islamic State group.

The Austrian national is believed to have been radicalized online. Ruf informs that chemical substances were found in his possession, which are currently being evaluated.

Swift has concerts scheduled at Vienna's Ernst Happel Stadium tomorrow, Friday and Saturday as part of her Eras tour.

Security measures will be strengthened during the concerts.

Ruf noted that there will be a special focus on entrance checks, among other things, and that concertgoers should plan for longer checks.

Vienna police chief Gerhard Purstl said that, while any concrete danger had been minimized, the abstract risk justified raising security.