"Odessa was attacked from the air," Anton Herashchenko, adviser to the interior minister, wrote on his Telegram account.

"Fires were reported in some areas. Some of the missiles were shot down by air defence."

An AFP reporter heard explosions in the southwestern city at around 6:00 am (0300 GMT).

The blasts sent up at least three columns of black smoke with flames visible apparently in an industrial area.

A soldier near the site of one of the strikes said it was likely a rocket or a missile.

The attack comes as Russian forces appeared to be withdrawing from the country's north.

On Friday, Ukraine's President Volodymyr Zelensky warned Russia was consolidating and preparing "powerful strikes" in the south, joining a chorus of Western assessments that Moscow's troops were regrouping.

Odessa, a historic city of around one million people, is Ukraine's largest Black Sea port.