UPDATE: Four female patients have been injured. They are all approx 17 year-old.
A tree branch has fallen on students at Heathcote High School in Sydney's south, reports Channel Seven.
NSW Ambulance crew was called to The Avenue at at HEATHCOTE at around 1.30pm today after a tree branch fell.
Ambulance officers have treated one patient with a head injury, two with back injuries. a fourth patient has unknown injuries.
They have all been transported to St George hospital.