More than 70 people were killed in Mogadishu on Saturday when a car bomb was detonated at a busy security checkpoint in the Somali capital.

At least 90 civilians, mostly students, were injured in the blast at the security and taxation checkpoint, Mogadishu Mayor Omar Muhamoud told reporters at the scene.

Security official Abdulahi Adan told the AFP news agency the blast came from a suicide bomb in a truck.

"Dozens of injured people were screaming for help, but the police immediately opened fire and I rushed back to my house," a witness told Reuters news agency.

No one immediately claimed responsibility for the attack, however, similar attacks are regularly carried out by the Al Qaeda-linked Islamist group al Shabaab, which wants to topple the United Nations-backed government in Somalia.