As we’ve been reporting, a fire has broken out in one of six nuclear reactors at the Zaporizhzhia power plant in southeast Ukraine.
Russian shelling on the facility continues and firefighters cannot get to the blaze yet, according to a plant spokesman.
Officials at the International Atomic Energy Agency (IAEA) as well as the US government have reportedly been in touch with Ukrainian authorities about the situation.
Graham Allison, a nuclear security expert at Harvard University, tells the BBC the reactor may melt down if the fire continues.
He warns that would prompt a release of radioactivity that contaminates the surrounding area for years, like during the 1986 Chernobyl disaster.
But Allison cautions that it is still far too early to know what is happening at the plant.
He says workers – Ukrainians and potentially Russians too – are likely “working hard together to prevent something catastrophic”.
The reactor in question is said to have been under renovation and that might suggest it contains less nuclear fuel, he noted.
Allison believes Russian forces may be trying to force the plant offline so as to cut off electricity in the surrounding area.
Ukraine’s regulator told the IAEA there has been no change reported in radiation levels at the plant site, the nuclear agency has tweeted.
Zaporizhzhia contributes about one-quarter of Ukraine’s power and is the largest in Europe.