Victoria Police’s major collision investigation unit is investigating Sunday’s head-on, two-car collision on the Western Highway two kilometres west of Stawell.

A Harrow woman, 51, died at the scene. Police have not released her name.

Stawell Acting Sergeant Pete Young said her husband, 57, was airlifted to Melbourne's The Alfred hospital in a critical condition.

The man had surgery for his injuries.

A hospital spokeswoman said the man remained in a critical but stable condition.

The second car contained a Rupanyup woman and two children aged five and six.

The two children suffered minor injuries.

They received treatment at Melbourne's Royal Children's Hospital on Sunday, before being sent home.

The Rupanyup woman was taken to Stawell District Hospital for observation but was later discharged.

Acting Sgt Young said the woman would assist police with their inquiries.

The road was closed until midnight, as emergency services investigated.

Police will prepare a report for the coroner.