An accident at a electrical substation, already damaged by Russian strikes, has left half a million households without power in the southern Ukrainian city of Odesa, authorities said Saturday.

"The situation is complex, the scale of the accident is significant," Prime Minister Denys Shmygal said on messaging app Telegram. He added that the substation had been "repeatedly" damaged as a result of Russian strikes.

Odesa region governor Maksym Marchenko described the accident as "serious," adding that the energy minister and the head of state-run electricity grid operator Ukrenergo had been sent to the city.

"A number of generators will be delivered to the region of Odesa within the next 24 hours," he said. "We expect the first generators to arrive tonight."

For months Moscow has systematically targeted Ukraine's energy grid, leaving millions in the dark and cold in the middle of winter.

The Black Sea port of Odesa was a favourite holiday destination for many Ukrainians and Russians before President Vladimir Putin sent troops to pro-Western Ukraine last February.

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An accident at a substation damaged by Russian strikes has left half a million households without power in the southern Ukrainian city of Odesa, authorities said on Saturday.