Crimea has been plunged into darkness after pylons carrying power lines which supply electricity from Ukraine were reportedly blown up on Saturday night.
All four power lines were cut, reports said, leaving the region’s two million inhabitants without electricity.
Images circulated on social media appeared to show Ukrainian flags attached to the damaged pylons.
Crimea was annexed by Russia last year, but the Ukrainian authorities have continued to supply power to the area.
“Crimea is completely cut off,” Viktor Plakida, the director of Crimea Energy, told Russia’s Tass news agency.
The Crimean Emergencies Ministry has reportedly declared a state of emergency and put rescue teams on high alert.
Medical facilities are connected to backup power supplies and their operations will not be affected, Mikhail Sheremet, Crimea’s deputy prime minister, said.
“Due to the complete shut-off from the Ukrainian power grid, the Crimean grid is operating in standalone mode,” Tass quoted a local emergency response unit as saying.
Two of the four power lines were cut in an explosion on Friday, according to earlier reports.
Ukrainian authorities said they encountered activists blockading the site when they tried to repair the damaged pylons.