STORY: Some of Europe's biggest banks are preparing for a winter of potential power cuts.

A number have prepared back-up generators, and got set to dim the lights at work so that online banking and ATMs don't go dark.

The aim is to support the money system that underpins the region's economy, as Russia cuts gas supply to Europe.

JPMorgan employs thousands in London and Frankfurt.

A source told Reuters it had practiced power outage simulations.

They also said the lender could change to diesel generators which could keep key offices running for several days.

Another source said Italy's UniCredit has tested its operational resilience this summer.

Its latest disaster recovery test focused on the resilience of data processing, the source said.

Deutsche Bank said it was rolling out energy saving measures across its 1,400 buildings in Germany.

It is shutting off hot running water in washrooms and changing workplace temperatures.

It also turned off all interior branch lighting and illuminated outdoor advertising overnight.

A number of banks have also cut office space and placed staff in fewer buildings.

Experts still fear that few companies are prepared for lengthy blackouts of more than a few days.

European gas prices have surged in recent months.

This week, Russia's state-controlled Gazprom said it would indefinitely extend a shutdown to the major Nord Stream 1 gas pipeline.