SYDNEY - A man has handed himself in to police and is being questioned after a fatal stabbing in Sydney's east, the New South Wales Police said on Monday.

The man in his 20s presented himself to St Marys Police Station in Sydney's west on Monday afternoon, police said.

Police and ambulance paramedics were called by a neighbor to a unit block on Mona Road in Darling Point at about 11 am local time on Monday.

On their arrival, police found a man with stab wounds at the apartment, accompanied by a woman who was suffering non-life threatening injuries.

They were treated by paramedics, but the man died at the scene, police said.

It's believed the couple were inside the unit when a man allegedly forced his way inside.

During the incident, the couple was injured before the man fled.

"There is a domestic relationship (between) the female and the man at St Mary's (police station)," Rose Bay Police Acting Superintendent Damian Henry told reporters.

"The full extent of those arrangements, it's early in the investigation, is yet to be determined."