Any city or corporation of fifty thousand inhabitants or more, having an improved wharf in suitable condition for receiving and discharging freight, may, if the annual tax levied by said city or corporation for municipal purposes on the class of property above described does not exceed one mill per dollar of the assessed valuation, charge and collect, for the maintenance and extension of said wharf, in addition to the tax assessed and collected for municipal purposes, a wharfage tax not to exceed three cents per ton, hull measurement, from all boats and vessels returned and assessed for taxation in said city, for each and every landing at the wharf of said city; provided, however, that from all steamboats and vessels not owned or registered within said city, or which have not been returned and assessed for taxation within said city, a wharfage tax, not exceeding five cents per ton, hull measurement, may be collected for each and every landing, to be applied to the building, repairing and maintaining of the wharf of said city.