Portugal's National Statistics Institute (INE) on Friday highlighted the "remarkable growth" of tourists from the United States visiting the country, which rose again in May by 18.3%.
According to INE, the Brazilian market accounted for the second highest increase, of 10%.
In the first five months of the year, the highest growth was seen in the same markets (20.5% and 12.6%, respectively) and also in the Canadian market (12.7%), INE said.
The top 15 issuing markets accounted for 87.3% of non-resident overnight stays.
The British market (with 22.7% of total overnight stays by non-residents) declined 9.0% in May, with a decrease of 7.4% in the first five months of the year.
The overnight stays by German visitors (14.1% of the total) increased 4.8% in May, although since the beginning of the year this market shows a slight decrease of 0.5%.
The French market (11.9% of the total) grew 1.1% in May. Between January and May, this market increased by 2.4%.
Overnight stays by residents of Spain (6% of the total) registered an increase of 5.7% in May and a slight decrease since the beginning of the year (0.3%).
According to figures released by INE on Friday, the hotel industry registered 2.0 million guests and 5.4 million overnight stays in May, corresponding to increases of 3.5% and 1.1%, against decreases of 5.2% and 8.3% in April.
Resident overnight stays rose 5.4%, while non-residents increased by 0.2% (-10.6% and -7.5% in April, respectively, a month affected by Easter), according to figures on tourist activity produced by INE.
The average stay (2.67 nights) fell by 2.4% (-1.5% for residents and -2.0% for non-residents) and the net bed occupancy rate (54.7%), fell by 0.4 percentage points.
