At least 65 people were killed on Tuesday when a suicide bomber detonated a car packed with explosives near the education ministry in Mogadishu, Xinhua reported.
More than 50 others, many of them students, were injured in the deafening explosion in the heart of the city.
"I can say that now we know 65 people dead and more than 50 others wounded in the attack," said Ali Muse, head of the emergency service.
Those at the scene reported bloody mayhem.
A witness, Omar Fidik, said: "We could hear the huge explosion around the ministry building. Dozens were killed, and charred bodies lay scattered in the area."
The explosion could be heard miles away.
Medical officials said the wounded were rushed to hospitals where doctors struggled to cope with the numbers.
Initial reports suggested that most of the wounded were students sitting for a foreign scholarship examination at the education ministry.
The attacks marks the first major assault by the radical Islamist group Al Shabaab since they withdrew from the Somali capital in August this year after a big government offensive to drive them out of the city.
Al Shabaab has often targeted Somali government as well as African Union peacekeeping forces.
A pro-Al Shabaab website described Tuesday's attack as "martyrdom operation", claiming that it targeted a ceremony at a government building where cabinet ministers were attending.
Somalia has not had a functional government since warlords ousted the government of Mohamed Siad Barre in 1991. Government forces have tried to restore order but without success.