* Spot at highest level since January
* Tight French nuclear remains key driver - trader
* German day-on-day wind power falls 7.4 GW
PARIS, Oct 6 (Reuters) - European prompt power prices for day-ahead delivery continued to rally on Thursday on firm demand, a sharp decline in German renewables output and unabated supply worries in France.
European power prices have surged in the past week over concerns that France, a net power exporter, and which depends on nuclear for about 75 percent of its electricity needs, could face supply constraints in the winter months and need to import more.
Traders said worries over French nuclear power supply remained the main driver.
The German spot hit levels last reached in January. The French day-ahead contract, which gained nearly 30 percent on Wednesday on reports of further unplanned outages at two power plants, also rose sharply.
German baseload power price for Friday delivery jumped 17.69 percent or 5.75 euros to 38.25 euros ($42.55) /MWh, before retreating slightly. The French contract gained 4.15 euros or 8.28 percent to 54.25 euros /MWh.
"The weather is getting colder and French nuclear availability remains weak," a trader said.
The French spot power price for early next week soared more than 45 percent on Thursday to 72 euros/MWh over the same concerns, the trader said.
German renewables power supply for Friday is expected to be weak. Wind power supply will tumble by 7.4 GW day-on-day to 6.8 GW, while although solar will add about 1 GW on Friday, it will remain at just about 2.5 GW, according to Thomson Reuters data.
Although consumption will fall slightly day-on-day on Friday, power demand is expected to remain firm at a combined 120 GW with heating demand rising as the weather gets colder.
Average temperatures are forecast at around 10.2 degrees Celsius in Germany and 13.3 degrees in France. Temperatures are expected to fall further in the coming week.
Prices along the forward power curve also posted gains on Thursday alongside coal, carbon and gas as French nuclear tightness provided support, while oil fell.
Oil futures dipped after Saudi Arabia trimmed the price of its flagship physical crude to Asia, but were still near more than three-month highs following a drop in U.S. crude inventories.
The German benchmark Cal'17 year-ahead baseload contract was up 75 cents or 2.46 percent at 31.20 euros a megawatt hour (MWh).
The less liquid equivalent French contract rose 1.3 euro or 3.27 percent to 41 euros /MWh.
Front-year EU carbon allowances jumped more than 6 percent to 5.81 euros a tonne.
Coal, which accounts for more than 40 percent of German power generation, rose 1.29 percent to $66.5.
In eastern Europe, the Czech year-ahead 2017 contract was up 0.48 percent at 31.15 euros /MWh.
The spot price for Friday gained 4.32 percent to 49.55 euros/MWh. (Reporting by Bate Felix; Editing by Susan Fenton)