Several districts of southern Paris were plunged into darkness on Thursday night due to a power outage tied to a technical glitch on an electrical transformer of energy supplier Enedis.

The incident comes amid worries that power blackouts could cripple infrastructure in France as the first cold snap of the winter tests the resilience of the power network.

Many streets in Paris’s third, fourth, fifth arrondissements were hit by the power cuts around 10:15 p.m. (2115 GMT) and power was restored around 11:00 p.m., grid operator RTE’s division for the region encompassing Paris, Ile de France, said on Twitter.

“Around 125,000 households were affected at the height of the incident,” it said.

A spokeswoman for Enedis told Reuters the transformer fault caused a break in a high voltage line.

She said the fault was not tied to a load-shedding exercise Enedis and RTE will carry out on Friday to prepare for possible controlled outages amid tight supplies.

“Today we are carrying out a crisis exercise as we routinely do,” the spokeswoman added.

Government ministers have warned of possible power outages in case of a gap between supply and demand, which they said would last no longer than two hours and be flagged in advance.

State-run utility EDF EDF.PA, a parent company of Enedis, is racing to get nuclear reactors hit by corrosion problems back on line.