Ukrainian authorities said on Saturday they were working to de-mine Kherson, record Russian crimes and restore power across the region one day after declaring the southern city had been liberated following months of Russian occupation.

Ukraine's president on Friday declared that the Black Sea city was back in Kyiv's hands after Moscow said it pulled back more than 30,000 troops from what was the first major urban hub to fall to Russia after the February assault.

Kherson was one of four regions in Ukraine that Russian President Vladimir Putin claimed to have annexed in September. But weeks later, the Russian retreat came as a huge boost to Ukrainians suffering from nearly nine months of fighting.

Ukrainians in Kherson danced around a bonfire and sang "Chervona Kalyna", a patriotic song, in the dark, in images distributed by the Ukrainian military.

After an eight-month Russian occupation, Ukrainian television resumed broadcasting in the city and the region's energy provider said it was working to restore power supplies.

Ukraine's police chief Igor Klymenko said around 200 officers were erecting roadblocks and recording "crimes of the Russian occupiers".

He urged Kherson residents to watch out for possible landmines laid by the Russian troops, saying one policeman had been wounded while de-mining an administrative building.

A woman and two children were taken to hospital with injuries after an explosive device went off near their car in the region's village of Mylove, police said.

In Berislav district of the Kherson region, Ukrainian police said Russian shelling left "dead and wounded," without providing further details.

On Saturday, Russia's former president Dmitry Medvedev hinted again that Moscow could use nuclear weapons.

"For reasons that are obvious to all reasonable people Russia has not yet used its entire arsenal of possible means of destruction," Medvedev said on messaging app Telegram.

"There is a time for everything."

Ukraine's Foreign Minister Dmytro Kuleba said Kyiv and the West were on their way to "joint victory" over Moscow after Russia's February 24 offensive.

"This is coming, and our victory will be our joint victory," Kuleba said as he met US Secretary of State Antony Blinken on the sidelines of a Southeast Asian summit in Cambodia.

"A victory of all peace-loving nations across the world."

Kherson's full recapture would open a gateway for Ukraine to the entire Kherson region, with access to both the Black Sea in the west and Sea of Azov in the east.

In Ukraine's capital, the news was met with joy late on Friday.

Wrapped in flags, popping champagne corks and belting out the national anthem, residents of Kherson living in Kyiv celebrated in the central Maidan square.

"I didn't believe it at first, I thought it was going to take weeks and months, a few hundred metres at a time, and now we see them arrive in Kherson in one day, it's the best surprise," said Artem Lukiv, 41, originally from Kherson.

Blinken hailed the "remarkable courage" of Ukraine's military and people and vowed US support "will continue for as long as it takes" to defeat Russia.

"It's a big moment and it's due to the incredible tenacity and skill of the Ukrainians, backed by the relentless and united support of the United States and our allies," added US National Security Advisor Jake Sullivan.

In London, British Defence Secretary Ben Wallace said Russia's "strategic failure" in Kherson could prompt ordinary Russians to question the war.

"Ordinary people of Russia must surely ask themselves: 'What was it all for?'"

Kuleba warned, however, that Russia is still "mobilising more conscripts and bringing more weapons to Ukraine" and called for the Western world's continued support.

The Kremlin has insisted that Kherson remains part of Russia.

"This is a subject of the Russian Federation. There are no changes in this and there cannot be changes," spokesman Dmitry Peskov told reporters.

A full Ukrainian recapture of the Kherson region would disrupt a land bridge for Russia between its mainland and the Crimean peninsula, which Moscow annexed in 2014. (AFP)