World leaders have accused Russia of endangering the safety of an entire continent after its forces shelled a nuclear power station in southern Ukraine.
A fire broke out at the Zaporizhzhia nuclear plant – the largest in Europe – after it was attacked by Russia.
Authorities say the facility is now safe and radiation levels are normal.
But UK Prime Minister Boris Jonson said the “reckless” attack could “directly threaten the safety of all of Europe”.
US President Joe Biden urged Moscow to stop its military activities around the site, while Canada’s Prime Minister Justin Trudeau said the “horrific attacks” from Russia “must cease immediately”. All three leaders spoke to Ukraine’s President Zelensky by phone.
Mr Zelensky, meanwhile, accused Russia of resorting to “nuclear terror” and wanting to repeat the 1986 Chernobyl disaster.
“If there is an explosion, it is the end of everything. The end of Europe,” he said.
A video feed from the nuclear plant showed blasts lighting up the night sky and sending up plumes of smoke.
Workers at the plant said the fire – which has since been extinguished – broke out at a training building outside the plant’s perimeter, and that only one of the plant’s six reactors were operational.
The UN’s nuclear watchdog, the International Atomic Energy Agency (IAEA), said the fire had not affected the plant’s “essential” equipment and there was no increase in radiation levels.
But the IAEA said it was in “full 24/7 response mode” due to the “serious situation” at the power station.
Ukrainian emergency services said initially they were blocked from getting to the scene of the blaze, prompting President Biden to publicly call on Russia to allow firefighters into the site.
Boris Johnson said he would seek an emergency meeting of the UN Security Council on Friday over the attack.
Experts said attacking a nuclear plant was unprecedented, and the situation was still very dangerous.
Dr Graham Allison, a nuclear security expert at Harvard University, said the “worst-case” would be if a fire at the plant caused a meltdown and prompted a release of radioactivity that contaminated the surrounding area for years.
But he also said it was more likely Russian forces were trying to “close down the supply of electricity to the surrounding area”, rather than attack the plant.
The plant, located around 550km (342 miles) south-east of the capital Kyiv, generates almost a quarter of all electricity in Ukraine.
Russian forces have already seized control of the Chernobyl nuclear plant, the site of the worst nuclear disaster in history.
News of the latest incident at Zaporizhzhia caused share prices in Asia to fall sharply.
More than one million people have fled Ukraine since the invasion began last week.
Despite punishing international sanctions, Russia’s President Vladimir Putin said his offensive was going “strictly according to schedule, according to plan”.
He has put his nuclear forces on high alert because of “aggressive statements” by the West.
Western ministers will hold crisis talks in Brussels on Friday as they seek to show their support for Ukraine.
UK Foreign Secretary Liz Truss called it “one of the biggest days of diplomacy” with allies prepared to “tighten the vice around Putin’s war machine” by targeting the Russian economy with more sanctions.