A toxic cloud of Saharan smog could hit the south of England today (May 5).

The Department for Food, Agriculture and Rural Affairs (Defra) has issued a warning of “moderate” air pollution for the south London, Kent and Surrey.

A health warning has been issued for those with lung problems.

Health advice states adults and children with lung problems, and adults with heart problems, should reduce physical exertion particularly if they are outdoors.

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People with asthma may find they need to the use their reliever inhaler more often, while older people should also reduce physical exertion.

The dust cloud is expected to become widespread, affecting much of England and Wales later today.

It is expected to continue from tomorrow until Sunday.

Smog - what you need to know

The dust phenomenon is formed when air pollution levels are high and there is not much wind, during pleasant weather conditions.

This causes a combination of nitrogen dioxide (NO2), particulate matter (PM10 and PM2.5) and ground level ozone to build up.

A yellowish or black fog is created, which can cause respiratory problems when breathed in.

Those suffering with lung and heart problems are particularly at risk.