21. (1) For the amount of all tolls, dues, rates and charges leviable under this Ordinance in respect of any goods, the Authority shall have a lien on such goods, and shall be entitled to seize and detain the same until such tolls, dues, rates and charges are fully paid. (2) For the amount of rent lawfully due on buildings, plinths, stacking areas and other premises which are the property of the Authority and not paid after demands therefor have been duly preferred, the Authority shall have a lien on all goods therein or thereon, and shall be entitled to seize and detain the same. (3) Tolls, dues, rates and charges in respect of goods to be landed shall become payable immediately on the landing of goods and in respect of goods to be removed from the premises of the Authority or to be shipped for export shall be payable before the goods are removed or shipped. (4) The lien for such tolls, dues, rates and charges shall have priority over all other liens and claims, except a lien for freight, primage and general average, where such lien has been reserved in the manner hereinafter provided, and the lien for money payable to the Government under any law for the time being in force.