File Photo: Ingoing and outgoing gas pipelines at a GRTgaz compressor station, in Morelmaison, eastern France. AFP
"Historic gas flows from the east have been reversed under the effect of the war in Ukraine," operator GRTgaz said in a statement.
It added that the firm "is working on adapting its network to develop new capacity for export from France to Germany, which will be available from mid-October."
GRTgaz said France's terminals for importing liquefied natural gas (LNG) were operating at 90 percent capacity, helping to fill the country's reserves to 94 percent -- around ten points higher than the European average.
In a "normal" winter, there would be "no shortage of gas", the company said -- while warning that "there is little room for manoeuvre, especially on days of especially high consumption".
And in the case of a "very cold" winter, GRTgaz expects a shortfall in gas supply of around five percent, a level it said "can be absorbed by reaching the energy saving objectives set by the authorities".
It encouraged households to follow advice to turn down their heating by one degree Celsius.
"As a last resort, load-shedding targeting major consumers could protect residential customers in extreme situations that are very unlikely to occur," the operator said.
The warnings come as Prime Minister Elisabeth Borne is set to lay out the government's plans for helping the country cope with surging energy costs this winter, caused by disruptions from Russia's invasion of Ukraine.