More than 1.6 million people are without power, water supplies to high-rise buildings have stopped and cable and mobile Internet is down.
The electricity feed from Ukraine was cut at 00:25 am (2225 GMT), the Crimean branch of Russia's emergency situations ministry said in a statement.
Crimea still depends on Ukraine for its electricity even after its annexation by Russia in March last year, a move which paved the way for the uprising in eastern Ukraine that has now killed more than 8,000 people.
"As of 1 pm (1000 GMT), 1,641,000 people have been left without electricity," and 150 schools have no power, Russia's energy ministry said.
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So far, Crimea has enough fuel to keep the gas and diesel-powered generators it has running for 29 days, the Russian authorities said.
An explosion on Saturday in Ukraine's Kherson region bordering Crimea cut the two working power lines to the peninsula, the state energy company Ukrenergo told Interfax-Ukraine news agency.
Two of the total four power lines had already been downed Friday in separate blasts.
"I had no electricity all night. These useless officials can't run the city and they still haven't built a local power station," said 49-year-old resident Konstantin.
"It's not the first time Ukraine has cut off electricity to Crimea, we are already used to power cuts and stock up on batteries," added Oleg, 56.
"The problem is the fridge keeps going off."
After the first attack on Friday, Ukrenergo posted pictures of a downed pylon and one with a hole blown through it.