Police at the scene of the accident in Caemawr Road, Morriston, Swansea.
Emergency services were called to a house on Caemawr Road in Morriston yesterday morning, and the woman - who is in her 50s - was taken to hospital.
Police have launched an investigating into what happened, and are still waiting to interview her.
It is believed the car at the centre of the probe was parked at the rear of the property when a section of the garden collapsed under it, causing the vehicle to partially fall into a hole injuring her.
A South Wales Police spokesman added: "Emergency services were called to Caemawr Road in Morriston on Wednesday morning following reports that a woman had suffered injuries after being involved in an incident involving a car at the rear of a house.
"The woman, who is in her 50s, has been taken to Morriston Hospital with serious injuries.
"An investigation to establish what happened is underway."
Police, fire and ambulance and the Wales Air Ambulance were called to the scene at 8.55am.
Last night the woman's condition was described as critical.
Comment: A rare earthquake also hit south Wales yesterday:
4.1 magnitude earthquake hits south Wales