Much of Europe is spending another day in the grips of bitterly cold weather that has engulfed much of the continent. And now officials are warning it may soon be even more difficult to find relief.

Power companies across Europe cut back on electricity exports, while warning domestic customers to conserve power where possible.

Frigid temperatures have caused a spike in demand for power to help heat homes and businesses, especially in parts of the Balkans that have been buried by blizzards.

Serbia – where much of the electricity is generated by coal – warned of restrictions and even threatened to shut off power to industrial customers if residents did not voluntarily cut back on usage. Officials say a large part of the problem is that temperatures have dropped so much the mining of coal has been slowed.

Problems have plagued Croatia and Bosnia, where hundreds of villages – and tens of thousands of people – have been cut off from supplies as snow continues to pile up. Bosnian rescue officials have been using helicopters to carry needed supplies to isolated hamlets. As of Wednesday, officials also said about half of the historic town of Mostar was without power.

The strain on resources is also being felt in Bulgaria, which said Thursday is was suspending electricity exports because of spiking domestic demand. Bulgaria helps supply power to Serbia, Macedonia, Greece and Turkey.

The brutal cold has also shut down some of the continent's most critical waterways.

At least four countries, Serbia, Croatia, Romania and Bulgaria, have banned shipping on the frozen Danube River for at least another nine days. The French news agency reported that Hungary was allowing ships on the river but only “at their own risk.”

Serbia has also banned all traffic on the ice-clogged Sava and Tisa rivers.

The death toll across Europe has climbed to more than 400 people, with more than one-fourth of the deaths coming in hard-hit Ukraine, where temperatures have fallen below minus 30 degrees Celsius.

Forecasters have warned it could be several weeks before the vicious cold departs. Some European officials have warned that even warmer temperatures may bring little relief, instead causing more damage and death as melting snow sends rivers over their banks.