Police in Alice Springs say would-be robbers picked the wrong victim to accost at the weekend.

A 20-year-old German woman was one of a group of tourists attacked by several people on the Wills Terrace footbridge on Saturday evening.

But Superintendent Sean Parnell told 783 ABC Alice Springs the woman was a black belt in karate.

"The victim there managed to punch one of the offenders three times in the face with a karate chop," he said.

"And they then attempted to run away and these baddies chased them and she's swung around and given them a kick to the side of the head and a couple more karate chops and they've run away."

He says she may have injured at least one of the attackers while fighting off the assault.

"We believe that, given the force she's hit him with, that he may have some injuries," he said.

"Be careful who you pick."