HELSINKI - Finns are well used to finding ways to stay warm, but soaring energy prices and the risk electricity blackouts this winter has pushed people in one of the world's northernmost countries to hoard firewood and refit their homes to cut power usage.

Finland's energy ties with neighbour Russia were cut after Moscow's invasion of Ukraine ten months ago, ending power and gas imports, while technical problems have limited output from a new domestic nuclear plant, triggering warnings of blackouts.

"Finland used to bring a third of its energy from Russia and now we are close to zero," said Riku Huttunen, director general of energy and climate policy at the Finnish ministry of economic affairs.

"One could say that if we have minus 20 degrees Celsius (-4 Fahrenheit) in the south and possibly minus 30 degrees up north, the risk of electricity shortage is very near," Huttunen told Reuters.

Foreseeing the danger of going into a brutal winter unprepared, Finns have since summer hoarded torches, heat pumps, timers, solar panels and of course, firewood, which is in plentiful supply as forests cover 75% of the country.

"We went three, four months without time off," said firewood producer Jari Saari, recounting how he received non-stop calls from customers looking to stock up.

"At one point we had 400 people waiting, I started to stress that what if I had promised to do too much," Saari said.

Rising costs of timber, transport and heating have pushed up the price, with a rough cubic metre of firewood now costing 120 euros ($128), up from a pre-crisis 85-90 euros, he said.

Mika and Satu Kirjavainen live in an old wooden cottage outside the capital Helsinki, where winter lasts around 100 days. The couple, both aged 54, used close to 1,600 kilowatt hours of electricity in December, but after their power company raised prices twice, they realised they were consuming far too much.

Their cottage, which is 100 years old, is now equipped with smart sockets, thick curtains that prevent heat from escaping, a new stove in the bedroom and two pipes that blow warm air from a heat storing fire place to other parts of the home.

"If the temperature does not drop (further), our total consumption will be just over 200 kilowatt hours this month," Satu Kirjavainen said.

($1 = 0.9391 euros)

(Reporting by Essi Lehto, editing by Terje Solsvik & Simon Cameron-Moore)