Heat warnings have been issued for cities across Italy and Spain, including popular tourist hotspots, as a heat dome hovering over southern Europe pushes temperatures above 40C. The region’s first heatwave of the year left urban areas sweltering over the weekend, with officials putting 21 Italian cities under “red alert”, 16 of which remained in place on Monday.

The designation indicates “emergency conditions with possible negative effects” on healthy people as well as those who are vulnerable through age or chronic illness. Regional governments in parts of Italy have also enforced restrictions on outdoor work, including construction and agricultural labour, during the peak hours of heat. Italian trade unions have reportedly been pushing authorities to enforce similar measures at a national level, as the heatwave shows no sign of abating.

Hospitals in Italy have recorded a surge in patients since the hot weather took hold, and several facilities, including the Ospedale dei Colli in Naples, have even created “heatstroke pathways” to streamline treatment for people affected by the high temperatures.

Other parts of southern Europe also hit record highs for June on the weekend, with 46C recorded in the southern Spanish province of Huelva on Saturday.

Spain’s national weather service has warned that no relief is expected until Thursday, with thunderstorm warnings also in place on Monday and heat alerts across the country coming into force on Tuesday afternoon.

Temperatures also rose to around 43C in Portugal on Monday, forcing authorities in the southwestern European country to issue red heat warnings for seven of its 18 districts, which expired at 9pm local time.