BILBAO, Spain — A fourth summer heatwave has hit Spain in recent days, with northern regions of the country sweltering in abnormally high temperatures of over 40 degrees Celsius on Sunday.

Temperatures soared over the weekend across Spain but especially in the traditionally cooler northern Cantabrian Sea area, triggering "extreme risk" alerts in the regions of Cantabria and the Basque country, weather service AEMET said.

People wore hats and cooled themselves with fans in the Basque country's Bilbao, one of the worst affected cities. "It's too hot, you can't just be in the streets, neither at the beach," Josefa Castillo told Reuters.

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Patrick Heremans, a Belgian tourist, was shocked by the heat: "We're unused to this kind of temperature, but we're going to the museum today, where there's air conditioning," he said.

Spain's health ministry told people to drink water, protect themselves against the sun and pay particular attention to the young and the elderly.

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According to the Spanish weather service, temperatures are expected to start lowering on Monday.