Forecasters said thermometers in Paris could break through the symbolic 40 degrees Celsius mark (104 Fahrenheit) -- which has happened only once before in the 130 years of modern-day record-keeping.

"The current heat is totally exceptional -- even for August," said Dominique Escale of state weather office Meteo France.

On Monday the southwestern city of Bordeaux saw temperatures of 40.2 degrees and Montauban in the Lot department -- a popular holiday destination also in the southwest -- hit 41.8 degrees. On the Atlantic sea-board temperatures were already 32 degrees at sunrise.

The dog days are caused by an anti-cyclone which has anchored itself firmly over the west European land mass, holding off rain-bearing depressions over the Atlantic and funnelling hot air north from Africa.

The effects of the weather pattern are aggravated by the long dry period that preceded it, meteorologists said. Because the landscape contains little moisture, less of the sun's energy is taken up in creating evaporation.

Though there was no clear evidence to blame global warming and greenhouse gas production, scientists at the World Meteorological Office point out that the world's ten hottest recorded years have all taken place since 1987.

Forecasters said there were no signs of the weather breaking and the heat was set to continue at least to the start of next week.

The punishing temperatures have sparked a spate of forest fires in Portugal, affecting 15 out of the country's 18 regions, which have killed 11 people. Last week fires in France killed five -- four of them foreign tourists -- and there have also been major blazes in Spain, Croatia and Italy.

Farmers in many countries are suffering the effects of severe drought and ozone concentrations have reached dangerous levels around some cities. In Paris, police were enforcing speed restrictions to cut the pollution.

Officials in Croatia said it was suffering the worst drought in 50 years, with the country's largest river the Sava at its lowest level in 160 years.

Experts said there was a risk some popular tourist areas such as the Adriatic islands could see shortages of drinking water.

Electricity production in France has been hit because rivers used to cool down nuclear powers plants are slow-moving and warm. Several stations are operating at low capacity.

Workers at the Fessenheim nuclear plant near the German border were dousing the outside of the reactor with water to keep it within regulation temperatures, prompting outrage from environmentalists who said it should be simply shut down till the heat subsides.

In Britain many trains were running at half speed because of fears the rails could buckle in the heat. The Czech Republic also ordered speed restictions after some track was seen to have twisted out of shape.

In Germany state workers in the capital Berlin were given the right to leave their desks once temperatures hit 29 degrees -- which they have -- on the grounds that working conditions are too difficult. It was unclear how many were taking advantage of the rule.

A mile-long island of sand has appeared in the North Sea off the German coast as a result of low water-levels, the British newspaper the Daily Telegraph reported.

Zoos were adapting novel ways of keeping animals cool. To the well-worn shower technique a park outside Paris added a new treat for polar bears: mackerel ice-lollies.

SPACE.WIRE