Electricity supplies from Ukraine to Crimea have been entirely shut off after the region's two remaining power pylons were blown up.
Russia's Emergency Situations Ministry has now declared a state of emergency in Crimea until power is fully returned.
The ministry did not say what had caused the outages, but Russian media reported that two pylons in the Kherson region of Ukraine north of Crimea had been blown up by Ukrainian nationalists.
This is believed to be the second such attack in a matter of days, affecting the two million people who live there.
Early on Friday morning, two of the four pylons connecting Crimea were brought down in similar circumstances - and Saturday night's attack means all power lines are now out of use.
It was not clear who carried out the attack but several pictures of the damage showed Ukrainian flags attacked to the wrecked pylons.
Video footage from a Tatar TV station posted on YouTube showed a group of activists clashing with members of Ukraine's national guard who attempted to seal the area around some of the damaged power lines on Saturday.
RIA Novosti news agency reported that the Crimean Tatars, an ethnic group native to the peninsula who oppose Russian rule, held a protest in favour of a blockade of Crimea.
Russia's emergency situations ministry said on Sunday morning they had managed to partially reconnect the cities of Simferopol, Feodosia, Yevpatoria and Yalta using generators.
But Russian news agency TASS reported that the gas turbines were providing less than half of the peninsula's needs.
Crimean Fuel and Energy Minister Sergei Yegorov said: "This morning, maximum consumption in the Crimean federal district is about 800 MW at such air temperatures. We have 350 MW of our own electricity generation and are short of another 450 MW."
Crimea’s First Vice-Premier Mikhail Sheremet said the peninsula has enough fuel to continue producing electricity for 30 days, TASS reported.
A system of rolling blackouts has been imposed and people have been told not to use electrical appliances.
Crimean website Krmyr.org reported that in city of Kerch, on the peninsula's eastern tip, there is no light or heating and water is at a reduced pressure.
Head of the city administration Sergei Pisarev told residents not to panic.
Crimea, which was annexed by Russia in April 2014, is dependent on Ukraine for electricity.
The attack, if by Ukrainian nationalists opposed to Russia's annexation of Crimea from Ukraine, is likely to further increase tensions between Russia and Ukraine.
