Collector Pooja Kulkarni, along with Deputy Tahsildar Jaishankar, her assistant and driver were on their way to Dharmapuri in a car when it rammed into a bus near a bus stand at Namasparai near Krishnagiri, police said.
The assistant, Muniraj, died while being taken to hospital, they said.
Kulkarni was taken to a government hospital at Krishnagiri, which referred her to a private hospital in Bangalore, they said.
Meanwhile, Chief Minister Jayalalithaa expressed shock over the accident and condoled the death of the assistant.
In a statement, she also announced a solatium of Rs one lakh to Muniraj's family from the chief minister's Public Relief Fund and wished the injured a speedy recovery.