Two teenage boys have been robbed at knife point of six boxes of Krispy Kreme doughnuts in Adelaide’s northwest, just days after the store’s opening.

Krispy Kreme opened its first South Australian store earlier this week on Port Rd, with some eager customers queuing outside for days before the opening.

Police allege a man approached the victims as they got into their car in West Croydon on Wednesday night, having just bought  doughnuts.

The man threatened them with what looked like a knife and took the doughnuts but did not demand anything else and the victims were not physically hurt.

The sweet toothed thief is described as a Caucasian man aged 16 to 20, about 165cm tall and wearing a black hooded jumper and black trackpants.

AAP