Dozens of storeys of the more than 200m-tall China Telecom building "burned with great intensity", sending thick smoke into the sky, state broadcaster CCTV said.
The fire has been put out, and no casualties have been found, according to Hunan's fire department.
It added that 36 fire trucks and 280 firefighters were deployed to the scene.
A photograph released by CCTV showed orange flames searing through the building in a built-up area of the city, as black smoke billowed into the sky.
A video posted on social media by a local news outlet also appeared to show the outside of the tower had been charred black.
Preliminary investigations showed that the outer wall of the 42-storey building caught fire, said Hunan's fire department. "At present, the open fire has been extinguished, and no casualties have been found," it added.
RHM/PR