The service said Wednesday's forecast sweltering temperatures of 37 degrees Celsius (99 Farenheit) could be matched on Thursday, extending a heatwave which has continued since the soccer World Cup began early last month.

"It has been going on pretty much non-stop since June 10," said Mueller-Westermeier. "It's far too warm and too dry in a lot of parts of Germany."

Shipping on the river Elbe -- which also runs through the Czech Republic and Poland -- was stopped as water levels dropped nearly 1 metre (yard) to around 95 centimetres in Germany.

"No cargo shipping is possible," said Herbert Dorf, a senior official at the Water and Shipping Bureau in Magdeburg.

There is a similar situation with the Oder river, which forms a stretch of the border between Germany and Poland.

Some nuclear power plants operating with river water cooling systems had to cut electricity output by up to 40 percent said Ivo Banek, spokesman for energy firm Vattenfall.

In order to protect their fragile ecosystems, rivers in Germany have limits on how warm water returning from power stations can be. Hotter rivers also mean soaring electricity prices, Banek said.

"There is no danger of a physical lack of electricity in Germany, but prices on the wholesale market have rocketed by 500 percent over the past weeks," he said.

In neighbouring Poland, fire and forest services said they had put 90 percent of the country on the top level of fire alert. Some southern districts have begun imposing limits on daily water usage, appealing to local residents to stop watering their gardens or washing cars.

"The suspicion is that some people are putting the welfare of their tomatoes first," one local mayor told the TVN news channel. "As a result in 10 days or so they may not have water to wash dishes or shower."

Experts also warned that food prices were set to rise as reports of crop failing amid the sweltering heat intensified.

A leading food industry group said Europe's shops and supermarkets are facing a shortage of vegetables later this year as a result of the current heatwave.

According to OEITFL, which represents Europe's fruit and vegetable processing industry, shop owners must prepare for the likelihood of empty shelves, fridges and freezers.

"The position is reminiscent of the catastrophic year 1976 when a comparable lack of rain was registered which now leaves them with less production than anticipated under normal weather conditions," said Susanne Meyer, OEITFL secretary general.

The heat wave has already taken its human toll. Some 40 people died over the past week in France and dozens more were killed by the scorching temperatures in the United States.