ANKARA - Witnesses reported hearing at least one blast in the Çukurambar region of the city.
Photos taken at the scene show smoke rising in the air and badly damaged buildings.
Ambulances have been rushed to the scene although no injuries have yet been reported.
The city's governor Ercan Topaca said the explosion had taken place at a tax office.
He said the building was empty and an investigation is now taking place.
Ankara Governor Ercan Topaca said: “The explosion was in the boiler room of the Çukramrambar Tax Office.
"The building is empty, the police are investigating at the scene".
One resident said on Twitter: "I can confirm I just heard the most enormous explosion in #Ankara. No idea what."
Another witness told BBC Turkey: “The explosion has totally destroyed the building. Buildings and cars within one kilometres have been damaged.”
“After the explosion black smoke rose from the building but there was no flame.”
Turkey has been hit by several terror attacks in recent months as well as an unsuccesful but bloody military coup in 2016.
Ankara 's parliament building was bombed during the July 2016 attempted putsch.