A Williamstown woman has been subjected to a terrifying home invasion, during which a masked man armed with a knife entered her house and stole her car.

The woman, 31, came home just before 4.30pm on Friday to find her Florence Street house trashed.

She said on social media she was initially unsure if it was a burglary, as all the family’s valuables were still around.

However, the filing cabinets and clothes cupboards had been pulled apart.

“I called my husband to check it wasn’t him, and during this time a man in a skeleton/Scream/Halloween mask walked straight into my front door, which was open.

“He had a knife and he approached where my four children and I were in the lounge room.

“He took my wallet and my car keys, and then walked slowly back out my house and drove my white Mazda CX-9 down Williamstown.”

The woman’s husband saw her car being driven by the thief in Champion Road as he returned home.

He followed it until it had a minor collision with another car near the Champion and Kororoit Creek roads intersection.

The thief then dumped the car in Gem Street and ran into another house, where he asked for a lift before fleeing towards Champion Road railway station.

Anyone with information is urged to contact Crime Stoppers on 1800333000.