Warrnambool police Sergeant Dave McDonald said the accident happened at 5.50pm on Wednesday evening.

He said the woman aged in her mid-60s was in a shed loading hay when two bales became unstable and fell.

"One landed on her and pinned the left side of her body," he said.

"She called a neighbour and emergency services were alerted. Police removed the bale and administered first aid.

"The woman suffered crush injuries and was airlifted to the Royal Melbourne Hospital."

The patient has been shifted from the Royal Melbourne's emergency department and is being treated for chest and spine injuries, a nurse confirmed on Thursday morning.

She is in a stable condition and is expected to remain in hospital for a number of days.

Sergeant McDonald said WorkSafe had been contacted, attended at the farm and would be investigating the circumstances of the accident.

Senior Constable Ross Hatton, of Warrnambool police, said the bale weighed around 500 kilograms.

"It was a big square bale, weighing approximately 500 kilograms," he said.

Brigades from Warrnambool, Mepunga, Naringal and Nullawarre responded to the Childers Cove Road incident along with SES paramedics and police.

"The Warrnambool SES was called to a rescue in Mepunga, where a lady collecting hay for her horses, was crushed by a massive hay bale," Warrnambool SES unit controller Giorgio Palmeri said.

"As soon as on scene, members of the Warrnambool SES worked together with local CFA and police to free the casualty.

"This was done by methodically disassembling the bale until it was small enough to be moved by hand. Once the casualty was stabilised by AV, SES members transported the casualty to the waiting ambulance to be then airlifted to a Melbourne hospital.

"Based on the latest reports, her injuries are not life-threatening and hopefully she will make a full recovery.

"We also made sure the area near Mepunga CFA station was safe for HEMS to land."

WorkSafe is making inquiries.

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