The tax should not be brought in until after the municipal elections later this year, however, he argued.

“It would not be right to launch it now”, a few months before the elections, Moreira said in a speech at an event in the city. "But I think that the tourist tax is an interesting subject to debate" with candidates for mayor.

Moreira was elected mayor of Porto four years ago as an independent, and is standing again this time.

He believes that revenue from the tourist tax should be used “to reduce the weight of the tourist footprint" - that is, the impact on the city of the growing influx of visitors - in order to avoid tourism taking on proportions seen in Barcelona, or indeed in parts of Lisbon, such as Mouraria, “in which it drives out citizens”.

Lisbon already has a tax on overnight stays in tourist accommodation in the city, or €1 a night. The funds are not earmarked for use in the way referred to by Moreira, and the impact of tourism in the capital has generated controversy.

Wednesday saw the introduction of a similar tax in Cascais, a city near Lisbon that has also seen a sharp increase in tourists in recent years.

According to Moreirea, Porto “is not in any phase of excess” in terms of tourism and “it's false” to say that the phenomenon is driving out locals.

“Until 2011 there was no tourist boom," he said, noting that in the decade to that year the city lost population, with the riverside parish of Miragaia losing 11% of its residents and neighbouring São Nicolau 25%.

He hailed the "enterpreneurship" shown by local companies in fostering and taking advantage of the growth in tourism.