Six people died when fire swept through a psychiatric hospital in the Ukrainian city of Odessa, authorities said on Tuesday.

The fire erupted late on Monday evening in the one-storey building, Ukraine's Emergency Service said in a statement. The cause was not immediately clear.

"Six people died and four have been hospitalised," the statement said. Nine other people escaped unharmed.

Ukrainian President Volodymyr Zelensky said he regretted the "terrible tragedy" and directed Prime Minister Volodymyr Groysman to set up a committee to investigate.

"The reasons (for the fire) will be established. I present my condolences to the families of the victims," he said on Twitter.

Deadly fires are not uncommon in Ukraine and other former Soviet republics due to outdated infrastructure and poor security measures.

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