Rescuers carried dead bodies past the twisted wreckage of a vehicle and a minibus taxi smeared with blood.
“So far, we’ve carried 61 dead people and 51 others injured. There are more casualties and the death toll is sure to rise,” Abdikadir Abdirahman Haji Aden, founder of Aamin ambulances, told Reuters.
No-one immediately claimed responsibility for the blast.
Al Qaeda-linked Islamist group al Shabaab regularly carries out such attacks in an attempt to undermine the government, which is backed by the United Nations and African Union troops.
The most deadly attack blamed on the group was in October 2017 when a bomb-laden truck exploded next to a fuel tanker in Mogadishu, creating a storm of fire that killed nearly 600 people.
While al Shabaab carries out frequent attacks, the death tolls are often lower than in Saturday’s blast. The group has sometimes not claimed responsibility for attacks that sparked a big public backlash, such as a 2009 suicide bombing of a graduation ceremony for medical students.
After the explosion at the Ex-Control checkpoint, 55-year-old Sabdow Ali, who lives nearby, said he left his house and counted at least 13 people dead.
“Dozens of injured people were screaming for help but the police immediately opened fire and I rushed back to my house,” he told Reuters.
Three other witnesses told Reuters that a small team of Turkish engineers were present at the time of the blast, constructing a road from the checkpoint into the city.
The witnesses said that a car belonging to the engineers was destroyed instantly in the blast. It was not clear whether the engineers survived.
Turkey has been a major donor to Somalia since a famine in 2011, and together with the government of Qatar is funding a number of infrastructure and medical projects in the country.
The checkpoint is also a tax collection point for the government, Ali Abdi Ali Hoshow, a foreign affairs ministry official, said on Twitter.
The injured were transported to Medina Hospital, where a Reuters witness saw dozens arriving by ambulance. A nurse at the hospital, speaking on condition of anonymity, said the facility had received more than 100 wounded people.
Relatives also gathered at the hospital, weeping outside the entrance as they sought information on their loved ones.
Speaking to reporters at the blast site, Mogadishu Mayor Omar Muhamoud said the government confirmed at least 90 civilians, mostly students, had been injured.
Police officials were not immediately available for comment on casualty numbers.
The Horn of Africa country has been riven by conflict since 1991, when clan warlords overthrew dictator Siad Barre and then turned on each other.
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