The names of ministers killed by the attack include Qamar Aden Ali, the country's health minister, Ahmed Abdulahi Waayeel, the minister of education, and Ibrahim Hassan Addow, the minister of higher education.
Saleban Olad Roble, the Somali sports minister, was also injured by the explosion.
Al-Arabiya, a Dubai-Based television network, said Hasan al-Zubair, one of its cameramen, had also been killed in the explosion.
The death toll is expected to rise.
The bombings happened during a graduation ceremony that ministers were attending.
Mohamed Adow, Al Jazeera's correspondent reporting from Kenya, said: "The graduation ceremony was for a group of medical students."
"Reports say that a man who dressed as a woman managed to pass through security checkpoints and enter the hallways of the hotel where he detonated himself as the ceremony was taking place," he said.
Adow said that there were reports of several journalists who were covering the ceremony that were also killed in the attack.
Suspicion for the blast immediately fell on the al-Shabaab group, which killed Somalia's security minister and at least 30 other people in the central town of Baladwayne in June.
"There has been no claims of responsibility for the explosion, but it has the hallmarks of al-Shabab which has so far been carrying out attacks over recent months," Adow said.
African troops protecting the fragile Somali government wage near daily battles with Islamist fighters who control much of central and southern Somalia.
The Horn of African nation has not had a stable government for almost