A woman has been injured after falling from the third floor of a unit block when a balcony collapsed during a housewarming party in Melbourne's south-east.

Firefighters and ambulance paramedics responded to the collapse in South Yarra late on Saturday night, extracting the woman from the rubble before she was taken to hospital.

The woman, aged in her 20s, had her fall broken by trees, possibly saving her from more life-threatening injuries, the Metropolitan Fire Brigade said in a statement.

Firefighters made the area safe and sealed off the entrance to the balcony.

AAP