An aerial photo shows a drought-affected forest with earlier fall-colour above the village of Roche, western Switzerland, on Tuesday. AFP

Nearly half of the European territory is in a state of drought due to low rainfall and heatwaves, according to a report by the science and knowledge service published on Tuesday.

The current drought appeared to be the worst in at least 500 years, the European Commission said in a statement.

The August report of the European Union (EU) agency said that 47 per cent territory of Europe has reached a warning level for drought, while 17 per cent of surveyed regions are in state of full alert.

An aerial photo shows low water levels in the Bough Beech Reservoir in Kent, UK. AFP

The report said dry conditions are related to scarce rain, and a number of heatwaves from May onwards that have affected river discharges widely across Europe.

The drought has substantially reduced yields for summer crop harvests, for grain maize set to be 16 per cent lower than the average of the previous five years and soybean and sunflowers yields set to fall by 15 per cent and 12 per cent respectively.

Soil moisture and vegetation stress are both severely affected, according to the report.

The rest of Europe, already affected by drought, maintains stable, severely dry conditions, according to the report.