Ukraine said Wednesday a short circuit at a nuclear plant posed "no threat" but had added to electricity shortages at a time when the country is struggling to keep the lights on.

The electrical fault at the Zaporizhya plant in the southeast of the country last Friday is due to be fixed in the coming days but comes as coal shortages are already forcing partial blackouts across Ukraine.

"The accident happened in the third block of the Zaporizhya nuclear power plant in the power output section. This is in no way associated with the reactor," Energy Minister Volodymyr Demchyshyn told reporters.

The plant was forced to shut down the affected generator, causing electricity shortages in the surrounding region.

Demchyshyn said tests would be run at the block over the next two days and "by Friday it will be working at full strength."

The government was forced to introduce rolling power cuts on Tuesday in response to the fault as well as rapidly diminishing coal stocks.

Ukraine gets just under half its electricity from nuclear stations and the rest from coal-fired power plants.

The conflict in the east of the country has already cut the government off from large swathes of the coal-rich mining region of Donbass.

Then, in late November, Russia announced without warning that it was stopping coal supplies to Ukraine, claiming "force majeure" but offering no explanation.

Experts say Ukraine is short some three million tonnes of coal for the winter season.

A statement on the Zaporizhya plant's website had said that production unit three had been disconnected from the power network until December 5 and that radiation levels around the plant were "unchanged".

Ukraine was the scene of the worst nuclear accident in history in 1986, when an explosion at the Chernobyl power plant in the north of the country released radiation across large swathes of Europe and the then Soviet Union.