Scotland Yard confirmed that there had been a number of casualties, including two people who were taken away from the scene by ambulance.
The area was evacuated and sealed off by police officers amid fears of a second explosion. However, they were unable to confirm whether the first blast had been caused by a bomb. Irish terrorism was ruled out.
The explosion was behind the Iceland store at the junction of Electric Avenue and Brixton Road, near to the entrance to Brixton market.
Police received the first reports of what had happened at 5.26pm and emergency services, including 20 fire engines, police explosives officers and helicopters, attended the scene.
One Brixton resident said: "The streets nearby were crammed full of buses and all the passengers were told to get off and move right away. I saw two people on stretchers taken away by ambulance."
A police spokesman was unable to confirm whether there had been a bomb, but windows in the area were said to have been blown out by the force of the explosion.
David Gledhill, a member of the public who was in the area at the time of the blast, said: "There was a huge explosion. Most of us thought it was thunder, but it was a very, very loud bang. It was definitely centred around Iceland. Glass was blown all over the place. Everything on the street stopped and people were getting off the buses.
"We heard that about 10 people had been injured. I could see stretchers coming out and being put into ambulances. We then heard that a second device had been found and they were moving everybody back again."Reuse content