Police have arrested a woman for stabbing a after a worker at the Ellenbrook Central Woolworths.

The staff member, aged in her 40s, was rushed to Royal Perth Hospital under priority 1 to Royal Perth Hospital, 6PR/Nine News reporter Sarah Smith told Oliver Peterson on Perth Live.

The shopping centre is currently still open while forensics are undertaking an investigation in Woolworths. Police are asking any eye-witnesses who saw a woman running from the store to provide details.

Sarah Smith later spoke to WA Police on Tuesday afternoon where they detailed the arrest of a Bullsbrook woman in her 30s.

She told Perth Live that the suspect approached the victim who was stacking shelves and stabbed her in the lower back in a "completely random and unprovoked attack."

The victim is undergoing treatment tonight.