A huge explosion rocked Somalia's capital Mogadishu early on Thursday, triggering a plume of smoke which rose from the blast site amid gunfire, according to a Reuters witness.
There was no immediate claim of responsibility but Islamist group al Shabaab frequently carries out bombings in the Horn of Africa country.
The blast which occurred near the K4 junction in the heart of Mogadishu was so huge it collapsed the walls of nearby schools and also left cars mangled.
"We were shaken by the blast pressure, then deafened by the gunfire that followed," Mohamed Hussein, a nurse at the nearby Osman Hospital told Reuters.
He added he had been pulled from the rubble of a collapsed ceiling.
"Our hospital walls collapsed. Opposite us is a school that also collapsed. I do not know how many died," he said.
Security officials could not be immediately reached for comment on what triggered the explosion and the casualties.
Al Shabaab has been fighting Somalia's central government for years to establish its own rule based on its strict interpretation of Islam's sharia law.