Faulty software in A4 models delivered after 2012 could prevent front airbags from deploying.
The airbag problem is caused by a software fault, affecting A4 saloons, station wagons and allroad models.
Audi said its faulty airbags are not made by Japan's Takata Corp, which is at the centre of a growing number of airbag recalls by various major brands.
Some 250,000 A4 models are being recalled in China, Audi's biggest market, and 150,000 in Germany, but no regional breakdown has been given for the remaining 450,000 cars.
The premium carmaker last week adjusted production of A4 models at its German plants adding new software.
There's as yet no word from Audi on whether Irish sold A4s are involved.
