Officials say the blast, also wounding more than 120 people, targeted a tax collection centre in capital and most of those killed were university and other students. Two Turkish brothers are among the dead.
A massive car bomb exploded in a busy area of Mogadishu on Saturday, leaving at least 79 people dead and scores injured in Somalia's deadliest attack in two years.
At least 16 of those killed were students from the capital's private Banadir University, who had been travelling on a bus when the car bomb detonated at a busy intersection southwest of the Somali capital.
Scores of wounded were carried on stretchers from the site, where the force of the explosion left the charred and twisted remains of vehicles.
Two Turkish nationals were also killed in the attack.
Police Captain Mohamed Hussein said the blast targeted a tax collection centre during the morning rush hour as Somalia returned to work after its weekend.
No group immediately claimed responsibility for the blast but President Mohamed Abdullahi Mohamed blamed the local Al Shabab militant group, which is linked to Al Qaida and whose reach has extended to deadly attacks on luxury malls and schools in neighbouring Kenya.
At least 125 people were wounded, Aamin Ambulance service director Abdiqadir Abdulrahman said.
Most of those killed were university and other students returning to class, Mayor Omar Mohamud Mohamed said.
A report by an international organisation, which did not want to be named, told Reuters news agency the death toll was actually more than 90 and that university students and 17 police officers were among those killed.
A Somali MP also tweeted that he had been told the death toll stands at more than 90.
TRT World spoke with Nairobi-based journalist Abdi Osman Adan for more.
Police officer Ibrahim Mohamed described the explosion as "devastating" and confirmed two Turkish nationals were among the dead.
"We have confirmed that two Turkish nationals, presumably road construction engineers are among the dead, we don't have details about whether they were passing by the area or stayed in the area," he said.
It was one of the deadliest attacks in Mogadishu in recent memory, and witnesses said its force reminded them of the devastating 2017 bombing that killed hundreds of people.
Erdogan condemns 'terrorist attack'
"I condemn the terror attack in Mogadishu, I wish Allah's mercy upon two Turkish citizens and Somalian brothers who lost their lives and speedy recovery for those who were injured," Turkey's President Recep Tayyip Erdogan wrote on Twitter.
Offering his condolences to the Turkish nation and Somali people, Erdogan said: "Turkey always stands by Somalia."
"Treacherous terrorist attack killed two of our Turkish citizens along with our innocent Somalian brothers and sisters. I pray for God's mercy. We will always stand by our brothers in Somalia. Our struggle against terror will continue with determination," Turkish Foreign Minister Mevlut Cavusoglu said in a statement.
"Our airplane loaded with emergency aid equipment and material belonging to the Turkish Armed Forces departed from Kayseri in order to provide emergency aid to our Somalian brothers injured in the despicable terror attack in Somalia," the Turkish defence ministry said.
Images from the scene showed the mangled frames of vehicles and bodies lying on the ground. At a hospital, families and friends picked through dozens of bodies.
"I saw many dead bodies lying on the ground," witness Mohamed Abdi Hakim said. "Some of those dead were police officers, but most of them were students."
"This explosion is similar to the one ... in 2017. This one occurred just a few steps away from where I am and it knocked me on the ground from its force. I have never seen such an explosion in my entire life," said witness Abdurrahman Yusuf.
"What happened today was horrible. I was among several students who rushed to the hospital after we have received the information. I have counted the dead bodies of 16 male and female students some of them had parts of their bodies severed," the student told AFP.
"The minibus carried 17 students and only one of them who had gotten off the bus before the blast to get a pass receipt from the tax collection point had survived," he added.
Al Shabab blamed for bombing
The latest attack again raises concern about the readiness of Somali forces to take over responsibility for the Horn of Africa country's security in the coming months from the AU force.
Officials blame Al Shabab which often carries out such attacks.
The terror group was pushed out of Mogadishu several years ago but continues to target high-profile areas such as checkpoints and hotels in the seaside city.
The terror group is now able to make its own explosives, its "weapon of choice," UN experts monitoring sanctions on Somalia said earlier this year.
The group had previously relied on military-grade explosives captured during assaults on an African Union peacekeeping force.
Al Shabab was blamed for the truck bombing in Mogadishu in October 2017 that killed more than 500 people.
The group never claimed responsibility for the blast that led to widespread public outrage.
Some analysts said Al Shabab didn't dare claim credit as its strategy of trying to sway public opinion by exposing government weakness had badly backfired.
Al Shabab, the target of a growing number of US air strikes since President Donald Trump took office, controls parts of Somalia's southern and central regions.
It funds itself with a "taxation" system that experts describe as extortion of businesses and travellers that brings in millions of dollars a year.