A teenager is in hospital with serious injuries after he was allegedly stabbed at a shopping centre in the Adelaide Hills.

Police have arrested and charged an 18-year-old man from the Adelaide Hills with aggravated assault causing serious harm.

They say the alleged stabbing occurred during an altercation between the two at Mount Barker Shopping Central at about 10am.

The two teenagers involved are known to each other.

Witnesses told 7News the alleged victim fled the scene on a pushbike, making his way to nearby Knott St where he collapsed and cried for help.

Police say the 17-year-old sustained life-threatening injuries, and was taken to the Royal Adelaide Hospital where he is in a serious but stable condition.

Anyone who witnessed the incident or has any information that could assist with the investigation and have not yet spoken to police has been asked to contact Crime Stoppers on 1800 333 000 or online at www.sa.crimestoppers.com.au

Police vehicles outside the shopping centre where the alleged stabbing occured. Photo: Jeff Anderson.