Russian forces have taken control of all administrative buildings in Ukraine’s city of Berdyansk, its mayor said Sunday.

Oleksandr Svidlo said in a video message on social media that they had seen Russian soldiers and heavy military equipment entering the city hours ago and they began advancing throughout the city.

"They informed us that all administrative buildings were under their control and that they were taking control of the executive committee building," Svidlo said.

"Tonight will be very, very hard," he added, calling on all residents to hide in shelters.

Berdyansk is a port city on Ukraine's southeastern coast with a population of over 100,000.