A fire in the tower in August 2000 killed three people and left the Russian capital without television broadcasts for several days.
The 1,771-foot tower in northern Moscow is one of the city's most notable landmarks. Its restaurant and observation deck were popular tourist sites, but were not reopened after the 2000 fire.
The Ministry of Emergency Situations confirmed to The Associated Press only that a small amount of smoke was seen coming from the tower and that its cause was being investigated.
News reports said the smoke was seen coming from about 1,120 feet up in the tower.
The ITAR-Tass news agency said the tower was being evacuated and the RIA-Novosti news agency cited an unnamed ministry source as saying the fire may have broken out in the insulation.