AFP reports that a car bomb hit a crowd of men enlisting into Yemen's Loyalist forces on Monday morning.
A security official told AFP that there were "dozens of casualties," but an official number has not been announced.
Aden is the seat of embattled President Abedrabbo Mansour Hadi's government and his Loyalist forces.
No group has claimed the attack, but al-Qaeda has conducted numerous suicide bombings in southern Yemen in recent months.
Loyalist forces and Houthi rebels are under a ceasefire while they negotiate peace talks in Kuwait. Though the Loyalist delegation temporarily withdrew from the peace talks, the ceasefire remains in effect.
Militant groups such a al-Qaeda and Daesh, both of which have gained a presence in Yemen, are not participating in the ceasefire.
