Surrey Fire Service has declared a major incident as crews battle an open fire, while crews in London battle two other large fires.
In Surrey, a fire at Hankley Common, near Farnham, has attracted “several fire engines” to the area.
The fire service tweeted: “There is a lot of smoke so please avoid the area, windows and doors should be closed if nearby and pets kept indoors “.
Read more: Dramatic satellite images show impact of heatwave as high temperatures hit country
Images online show plumes of smoke rising over the county, with people as far away as Guildford reporting seeing it.
It comes after a spate of wildfires in and around London after last week’s record temperatures left the earth box dry.
Firefighters in London are also battling bushfires, with fires at Rammey Marsh in Enfield and Cranford Park in Hayes.
In Enfield, near Epping Forest, London Fire Brigade (LFB) said around 100 firefighters were battling the grass fire, which had grown to the size of four football pitches.
The service urged people to help prevent further fires by not having barbecues and disposing of cigarettes properly.
A fire in Hayes can be seen from west London, with the LFB adding that 70 firefighters are at the scene. He says people in the area should close doors and windows.
The UK hit record temperatures on Tuesday, with Coningsby in Lincolnshire hitting 40.3C (104.5F), the first time since records began that the mercury has topped 40C in the country .
Parts of the UK suffered significant damage as a result of the extreme heat, including house and bushfires, melting of airport runways and expanding railway tracks.