Police suspect illegal drugs were used moments before a woman was shot dead - possibly accidentally - at a house in Melbourne's west.

A man shot the 21-year-old Keilor Downs woman at a house in Currumghi Circuit, St Albans, just after 5am (AEST) Sunday before fleeing in a red car.

A hunt is now under way for the man. Police said the pair knew one another.

Homicide squad Detective Senior Sergeant Rod Iddles said there may have been some illicit drug use at the house, but did not believe the dispute was about drugs.

He said police will explore every avenue, including that the shooting was accidental.

"Here we have a 21-year-old girl, not even in the prime of her life, and her life's been taken away," Det Sen Sgt Iddles told reporters.

"There may have been some illicit drug use; during the course of that a gun's been produced, and at this stage I can't tell you whether it's gone off accidentally or deliberately."

The offender is described as Caucasian, in his early 20s, 195cm tall with a solid build and dark hair.

The small red car he fled in is believed to be a Toyota.

Police are appealing for the man to hand himself in to any police station.

Anyone with any information is urged to contact Crime Stoppers.