The tallest structure in Europe and Asia, Ostankino Tower, caught fire on Friday afternoon in Moscow, Russian emergency officials said.
The 540-metre tall television tower caught fire at a height of 340 metres, Natasha Lukash, spokeswoman for the country's Emergency Situations Ministry, told Itar-Tass.
"The reason is now being investigated," she said. Government television and radio officials said the fire was unrelated to the tower's broadcasting functions and that it began on a balcony outside the tower.
The building was quickly evacuated, Moscow fire safety officials told Interfax. Over 20 fire fighting brigades were on the scene within half an hour of receiving a call from the tower.
The fire's severity was played down in immediate reports, with fire fighters calling it a second-degree incident, on a scale of one to five.
The world's tallest freestanding structure when it was completed in 1976, Ostankino is currently second to Toronto's CN Tower.
The tower has been closed to tourists since a 2000 fire killed three people and was to be opened again for visitors later this year.