Swansea's Indoor Market and bus station were also closed but officers reopened affected areas just before 17:00 BST.
South Wales Police had received reports of a suspect package at about 14:00.
They said the incident had caused "significant disruption".
Bus operator First Cymru said services were returning to normal but delays may continue.
A police spokesman said: "While we ask people to be vigilant, we will take robust action against anyone who causes significant disruption through hoax activity."
A man has been arrested following the evacuation of Swansea's Quadrant shopping centre after reports of a suspicious package "turned out to be a hoax".