The Alentejo and Tagus Valley region are forecast to see temperatures rise to between 40 and 45 degrees.

Parts of the Algarve can also expect uncomfortable levels of heat, with the Met Office forecasting that Silves will see highs in excess of 40 degrees Celsius for seven straight days starting this Thursday.

Southern Portugal will see the sky turn yellow from Wednesday as a southerly wind brings with dust particles from the Sahara desert.