The emergency services responded to the stabbings near a school on Power Street in Doonside, a suburb located approximately 35 km west of Sydney's central business district, Xinhua news agency reported.
Before police officers arrived, two boys in their teens had presented themselves to the Blacktown Police Station with stab wounds.
Both received treatment at the station. But one boy later died at the scene, while the other was transported to a hospital in a serious condition.
Police have established multiple crime scenes, with investigations launched into the circumstances surrounding the incident.
New South Wales Police Force confirmed in a statement that one person has been arrested and inquiries are ongoing.