There has been a large explosion in the Ethiopian capital's crowded Merkato business district where people gather socially after work.
The BBC's Elizabeth Blunt in Addis Ababa says the blast happened in a video parlour.
A local radio station said that four people were killed and another 24 were wounded. The police have not released any figures.
Sporadic attacks are usually blamed on Eritrean-backed rebels.
Tensions between the two countries stem from Ethiopia's failure to hand over the disputed border town of Badme, which a UN-backed commission awarded to Eritrea.
The two countries fought a bloody war between 1998 and 2000.
Our correspondent says the explosion happened at around 1700 local time (1400 GMT).
Lots of ambulances rushed to the scene - between the main Friday Mosque and bus station - and the whole area was cordoned off by police, she says.