The attackers targeted a small restaurant at lunch hour that is popular with government officials, about 1 kilometer from the presidential palace in the heart of Mogadishu.
The explosion also hit a small tea shop next to the restaurant and sent a huge plume of smoke above the city which lies on the Indian Ocean.
"The death toll is sure to rise," said Police Colonel Osman Ibrahim at the scene. Police said was the attack was a suicide bombing.
No group has claimed responsibility but previous bombings in Mogadishu have been carried out by the Islamist al Shabaab rebel group.