KYIV (REUTERS) - The Russian-occupied Zaporizhzhia nuclear power plant resumed electricity supplies to Ukraine on Friday (Aug 26) after one of its six reactors was reconnected to the Ukrainian grid, state nuclear company Energoatom said.

Europe's largest nuclear power plant, which is located in southern Ukraine, was disconnected from the Ukrainian grid for the first time in its history on Thursday after a fire caused by shelling damaged a power line, Kyiv said earlier.

"The Zaporizhzhia nuclear power station is connected to the grid and is producing electricity for the needs of Ukraine," Energoatom said in a statement on Friday.

Russia, which invaded Ukraine in February, took control of the nuclear plant in March, though it is still operated by Ukrainian technicians working for Energoatom.

The nuclear plant supplied more than 20 per cent of Ukraine's electricity needs before the war and its loss would pile new strain on the government, which is already bracing for a difficult wartime winter of potentially crippling energy shortages.

Ukraine's President Volodymyr Zelensky said the world narrowly escaped a radiation disaster when electricity the nuclear power plant was cut off for hours and he urged international bodies to act faster to force Russian troops to vacate the site.

Mr Zelensky said Russian shelling on Thursday had sparked fires in the ash pits of a nearby coal power station that disconnected the Zaporozhzhia plant from the power grid. A Russian official said Ukraine was to blame.

Back-up diesel generators ensured power supply vital for cooling and safety systems at the plant, Mr Zelensky said, praising the Ukrainian technicians who operate the plant under the gaze of the Russian military.

"If our station staff had not reacted after the blackout, then we would have already been forced to overcome the consequences of a radiation accident," he said in a video address on Thursday evening.

"Russia has put Ukraine and all Europeans in a situation one step away from a radiation disaster... Every minute that Russian troops remain at the nuclear power station there is a risk of a global radiation catastrophe," he said.

Residents in the capital Kyiv, some 556km to the northwest of the plant, expressed alarm at the situation.

"Of course everyone is afraid, the entire world is afraid. I really want the situation to become peaceful again," said businessman Volodymyr, 35, who declined to give his last name. "I want the power shortages to be overcome and additional facilities to be operational."

Mr Vladimir Rogov, a Russian-appointed official in the occupied town of Enerhodar near the plant, blamed Ukrainian armed forces for Thursday's incident, saying they caused a fire in a forest near the plant.

"This was caused by the disconnection of power lines from the Zaporizhzhia nuclear power station as a result of provocations by Zelensky's fighters," Mr Rogov wrote on Telegram.

"The disconnection itself was triggered by a fire and short circuit on the power lines."

Russia's Defence Ministry said on Friday its forces had destroyed a US-made M777 howitzer which it said Ukraine had used to shell the Zaporizhzhia plant. Satellite images showed a fire near the plant but Reuters could not verify its cause.

Energoatom said Thursday's incident had been the first complete disconnection of the plant, which has become a hotspot in the six-month-old war.

The regional authorities in Zaporizhzhia said more than 18,000 people across several settlements remained without electricity on Friday due to damage caused to power lines, without specifying which lines they meant.

A Reuters cameraman said there was electricity as normal in the city of Zaporizhzhia on Friday.

The United Nations is seeking access to the plant and has called for the area to be demilitarised. International Atomic Energy Agency (IAEA) officials are "very, very close" to being able to visit Zaporizhzhia, agency Director-General Rafael Grossi said on Thursday.

Germany on Friday condemned Russia's continued occupation of the plant.

"The situation (there) is still very, very dangerous," a foreign ministry spokesman said.

Nuclear experts have warned of the risk of damage to the plant's spent nuclear fuel pools or its reactors. Cuts in power needed to cool the pools could cause a disastrous meltdown.

Dr Paul Bracken, a national security expert and professor at the Yale School of Management, said the concern was that artillery shells or missiles could puncture the reactor walls and spread radiation far and wide, much like the 1986 accident involving the Chernobyl reactor.

A failure at the Zaporizhzhia plant could "kill hundreds or thousands of people, and damage environmentally a far larger area reaching into Europe", Dr Bracken said.

"Russian Roulette is a good metaphor because the Russians are spinning the chamber of the revolver, threatening to blow out the brains of the reactor all over Europe," he said.