The blast shook the Somali capital Mogadishu early Thursday, causing heavy smoke from the blast site, amid gunshots, according to a Reuters witness.
There have been no immediate claims of responsibility, but the Islamist group Al-Shabaab regularly carries out bomb attacks in the Horn of Africa country.
The blast near the K4 junction in central Mogadishu was so severe that it knocked down nearby school walls and left vehicles damaged.
“We were shaken by the explosion pressure, then stunned by the ensuing gunfire,” Mohamed Hussein, a nurse at a nearby Osman hospital, told Reuters.
He added that he had been released from the rubble of a collapsed ceiling.
“The walls of our hospitals have collapsed. In front of us is a school that also collapsed. I do not know how many died, ”he said.
Security officials could not immediately be reached for comment on the cause of the explosion.
Al-Shabaab has fought for years against the Somali central government to establish its rule based on its strict interpretation of Islamic Sharia law.