Fire has engulfed almost every floor of the tallest building in southern Russia.
The building, in the Chechen Republic capital of Grozny, includes luxury apartments and a five-star hotel.
REUTERS, Yelena Fitkulina
Local authorities have said that the tower has been evacuated of people and no casualties have been reported.
Firefighters managed to extinguish flames on the lower floors, but the blaze spread very quickly and soon neared top of the enormous structure.
Helicopters have been sent from the southern city of Pyatigorsk to help out.
State television pictures showed a huge cloud of smoke rising into the sky and clinging to the side of the vast building.
"Witnesses reported smoke pouring out from the fourth and fifth floors," the ITAR-TASS news agency said, quoting the Emergency Situations Ministry.
But there were conflicting suggestions over where fire had begun, with eyewitnesses saying they had seen flames begin at both the top and the bottom of the tower.
The building is the centrepiece of the Grozny-City complex, which was partly opened in 2011.
In one of the adjoining skyscrapers is an apartment reportedly belonging to French film star and tax exile Gerard Depardieu.
When complete, the entire complex will apparently boast 1,000 apartments.