The military spokesman said the blast happened when staff at the clothing store checked a suspicious parcel that had been left behind at the baggage counter.
"Sixteen people were brought in dead," the spokeswoman at Kalubowila Hospital, located near where the explosion took place, told the AFP news agency by telephone.
A bus caught fire as a result of the explosion, the defence ministry said, and the hospital spokeswoman said more casualties were feared.
It was the second attack in the capital and came a day after Tamil Tiger rebel leader Velupillai Prabhakaran vowed to hit back at the government.
On Wednesday monring a Tamil Tiger suicide bomber blew herself up near the office of a government minister from a rival Tamil group.
Authorities believe that the attac