Italy is placing nearly all of its major cities under the highest alert for heat from Monday, as a fresh heatwave grips the country, authorities said on Saturday.

Temperatures were forecast to reach into the high 30s Celsius on Monday, the health ministry said.

Out of the nation's 27 major cities only two -- Reggio Calabria in the southern tip of Italy's "boot" and Messina, facing it across the strait in Sicily -- were not being placed on highest alert for heat, it said.

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After hitting western Europe at the start of last week, the season's latest heatwave roasted central Europe and on Saturday began to reach into Italy.