Germany has been forced to call upon its reserves for producing electricity for the second time this winter as Europe is gripped by a severe cold snap, officials said on Thursday.

The country's four main power operators requested the reserve generator at a coal-powered plant in southern Germany and two plants in Austria be activated, the regional environment ministry in the southern state of Baden-Wuerttemberg said.

The power station in Germany, in the southern city of Mannheim, would continue to be used Thursday, a spokesman said.

"We do not have a problem of supply, of quantity, it's principally a question of stabilising the network," a spokeswoman for the Germany electricity market regulator said.

Germany also had to tap its reserves in early December. The system was set up in August to avoid shortages and stabilise the network for the country's winter power provision.

Under the reserve plan, five generators in Germany have been designated, which are powered by coal or gas and normally not in operation, as well as several in neighbouring Austria.

They can only be used at the request of the electricity network operators in case of need or as a preventive step.

In the wake of the devastating earthquake and tsunami in Japan last March, which prompted radiation to leak at the Fukushima Daiichi nuclear plant, Germany decided to phase out nuclear power by 2022.

Eight of Germany's 17 reactors have already been switched off and the nine reactors currently on line are due to be turned off between 2015 and 2022.