Northern Territory Police are calling for witnesses to come forward after a woman was assaulted while she was running yesterday afternoon in Alice Springs.

Police said the woman was running along the Todd River, near the Stott Terrace Bridge about 3.45pm.

Police said a young man travelling on a black bike was travelling nearby, and that he allegedly indecently assaulted the woman.

The youth has been described as tall with tanned skin.

He was said to be wearing a black shirt with the white numbers "2000" on the back.

Anyone with further information has been urged to come forward to police.

DOWNLOAD THE 9NEWS APP: Stay across all the latest in breaking news, sport, politics and the weather via our news app and get notifications sent straight to your smartphone. Available on the Apple App Store and Google Play.