A heatwave that has pushed temperatures above 40 degrees in parts of western Europe this week continues to prompt authorities to warn people to take precautions to stay safe during the soaring heat. Forty people have drowned in France since the middle of last week in rivers, seas and lakes, as they tried to cool down and escape the spiking temperatures, which hit highs of 44.3 degrees on Tuesday. Vast swathes of the country are sweltering under temperatures in the high 30s and above, in an “unprecedented” heatwave that has closed schools and disrupted public transport networks. Météo-France, the national weather forecasting institute, said overnight temperatures on Monday were the highest since recorded measurements began in 1947. That followed earlier record-breaking afternoon temperatures that hit 37.8 degrees. French meteorologists have estimated the first four days of this week may rank among the hottest ever recorded in France for this time of the year. More than half of the country’s 101 administrative regions are subject to a status red heatwave alert, which Météo-France said was also “unprecedented”. French sports minister ​Marina Ferrari said she understood the urge to escape the heat but warned members of the public against swimming in dangerous or unauthorised areas. The Louvre Museum in Paris announced it will close its doors two hours earlier for the rest of the week, to manage a build-up of heat in parts of the “historic” building, which it said was “exacerbated by the high volume of visitors”. [ In pictures: Europe swelters in heat domeOpens in new window ]Spain’s meteorological agency has placed a large number of regions on alert, warning of dangerous heat. Temperatures are expected to reach 44 degrees in one southern pocket of the country. In response to the high temperatures, Madrid has opened “climate shelters” for the city’s homeless population and other vulnerable groups. Children cool off as they play football under a fountain next to the Manzanares river in Madrid, Spain. Photograph: Getty Images The Italian government passed a decree allowing some businesses to access a fund to send staff home with pay, or reduce their hours, during the heatwave, the Italian news agency Ansa reported. Rome, Milan, Florence, Turin, Venice and 10 other Italian cities were subject to the state’s highest level of alert, meaning the heat is deemed to pose a risk to the general population. The UK Met Office expects the existing record for the highest daytime temperature in June – a reading of 35.6 degrees taken during a 1976 heatwave – will be broken this week. “Around the world climate disasters are becoming more frequent, more destructive and more costly,” United Nations secretary general, António Guterres told a climate conference in London, while the city was gripped by suffocating heat. “London isn’t just calling, it’s cooking,” he said. Guterres said a climate crisis created by the consumption of fossil fuels was pushing the world towards “catastrophic” tipping points. Authorities in Luxembourg sent out an emergency text alert across the country’s mobile phone networks, telling the public to take precautionary measures. The alert said high temperatures posed a “significant danger” over the coming days and advised people to avoid spending long periods outside during the hottest hours of the day. A Met Éireann high-temperature alert kicked in at noon on Tuesday, and runs until Friday, with a daily high of 28.3 degrees recorded at the Phoenix Park in Dublin. Sunbathers at Seapoint in Dún Laoghaire. Photograph: Niall Carson/PA Wire