- Around 50 people have been killed and dozens more injured, activist says
- There's been no claim of responsibility for the reported blast
An earlier report from the Aleppo Media Center activist group put the death toll at 21, with dozens injured.
Another local resident told CNN the explosion occurred around 11:40 a.m. local time near the courthouse and grocery market, and that it was caused by a truck bomb.
"My house is near the explosion area, and the sound of the blast was so huge," said Rahhal, who asked that his full name not be used for safety reasons.
Rahhal said he had seen at least seven dead bodies before medics moved him away.
He also said he blamed the rebel Free Syrian Army -- which controls the area -- for not taking enough security precautions despite having many checkpoints.
There has been no claim of responsibility so far, but ISIS car bombs have targeted the city, near the Turkish border, in the past.
The reported violence comes despite a nationwide ceasefire
, brokered by Russia and Turkey, that has largely held since coming into force December 30.