Iraqi Prime Minister Haider al-Abadi has ordered all government staff to take Thursday off work because of exceptionally high temperatures.
Forecasters expect air temperatures in the capital, Baghdad, to reach 50C (122F) on Thursday afternoon.
Heatwave conditions are also expected in the cities of Basra and Mosul.
The extreme heat can cause chronic power shortages, depriving homes and businesses of electricity and air conditioning for parts of the day.
Near record temperatures are being experienced across the region and have also affected parts of Europe in recent weeks.
Scientists warn that extreme weather could lead to the deaths of 52,000 people yearly in Europe by 2100 if nothing is done to halt the effects of climate change.