Red alerts for extreme heat are in place in most of Italy's main cities as a heatwave intensifies in Europe.

Temperatures are expected to peak on Wednesday, with 23 cities on high alert - from Trieste in the north-east to Messina in the south-west.

The warnings mean the heat poses a threat to everybody, not just vulnerable groups.

Wildfires are also raging across the continent, including in Greece and the Swiss Alps.

Millions of people in the northern hemisphere are being affected by scorching temperatures.

It is being caused by a high pressure system bringing warmer, tropical air, south of a jet stream currently stuck over central Europe.

And the heat is forecast to last through Wednesday across most of southern Europe, following several days of temperatures in excess of 40C (104F).

BBC Weather says parts of the Italian islands of Sardinia and Sicily will be the hottest again, with highs of around 46C or 47C.

The heatwave, which has swept across the country, has been described by local media as settimana infernale - or "week of hell".

The Italian health ministry has asked emergency rooms across the country to activate so-called "heat codes", assigning a separate group of medical staff to treat people who come in with symptoms caused by the heat.

Similar measures were brought in at the start of 2020, when Italy became the epicentre of the Covid pandemic in Europe.

There has been a 20% increase in the number of patients being admitted with heat-related symptoms, such as dehydration, exhaustion, heat stroke, and confusion, according to the health ministry.

A new record-high temperature of 41.8C was reportedly measured in the capital Rome on Tuesday.

There have also been power cuts in Palermo, Sicily's capital, as a result of high demand for air conditioning.

Red alerts also remain in place across Spain, Greece and parts of the Balkans.

Temperatures are expected to fall on Thursday for many in Europe, including northern Italy - where red alerts will be removed for six cities.

But BBC Weather's Matt Taylor says that temperatures could be in the mid to high 40s for many in the central and eastern Mediterranean by the weekend and carrying on into next week - which could potentially come close to breaking records.

Tunisia in North Africa is also expected to register 50C in some spots, he added.

The UN weather agency, the World Meteorological Organization, has warned that the heatwave in Europe could continue into August, and that the extreme temperatures sweeping the globe are the new normal in a world warmed by climate change.

In Greece, staff at the Acropolis in Athens, one of Greece's top tourist attractions, will stop working for four hours a day from Thursday in protest at working conditions during the heat, a union representing its workers has said.

The ancient site, which has seen a major rise in visitor numbers in recent months, is normally open from 08:00 to 20:00 local time every day, but the protest will see workers stop working at 16:00.

Multiple wildfires have also swept across the country since Monday - including one which led to the evacuation of 1,200 children from a summer camp.

The most severe fire burned in the Dervenochoria region, north of Athens. Others also continue to rage in the towns of Loutraki - near the city of Corinth - and in Kouvaras, south of the capital.

The Spanish island of La Palma has been left devastated by wildfires, which have now been brought under control thanks to cooler overnight temperatures.

The fires destroyed some 3,500 hectares (8,700 acres) of land, burned around 20 houses and buildings and forced 4,000 residents to evacuate.

Extreme temperatures have also gripped other parts of the globe including the US and China.

More than 80 million people in western and southern US states are under advisories for a "widespread and oppressive" heatwave.

The city of Phoenix, Arizona, on Tuesday exceeded 43C for the 19th consecutive day, breaking its all-time record of 18 straight days.

In China, Beijing has registered a record 27 days of temperatures above 35C (95F).

Scientists have long-warned that climate change will make heatwaves more frequent, more intense and last longer in duration.

Experts say Europe in particular is warming faster than many climate models predicted.

More than 61,000 people were estimated to have died from the heat in Europe last year, and there are fears this year will be similar.