A woman, believed to be in her 30s, has blown herself up in central Tunis in front of a shopping centre, according to Tunisian state radio.
There were no immediate reports of fatalities but nine people were injured in the blast, the Tunisian interior ministry said.
Eight of those injured are believed to be police officers.
A witness reported an explosion on the central Habib Bourguiba avenue and police were seen cordoning off the area.
Soon after the explosion ambulances could be heard rushing to the scene.
"I was in front of the theatre and heard a huge explosion and saw people fleeing," witness Mohamed Ekbal bin Rajib told Reuters.
Habib Bourguiba avenue, where the explosion took place, is considered the cultural, political and economic heart of Tunis and is sometimes called Tunisia's Champs Elysees.
Tunisia, which is heavily dependent on tourism, has improved security since a series of militant attacks targeting tourists caused the near collapse of the sector three years ago.
In 2015, 21 people were killed during a hostage siege in its national museum, the Bardo in Tunis, and a gunman killed 38 people on a resort beach.
There have been no attacks on that scale since then, but the economy has remained troubled and the authorities worry about militants who shelter in neighbouring Libya.
Agencies contributed to this report
