This was announced by the mayor of Mykolaiv Oleksandr Senkevych on Telegram.
"Powerful explosions were heard in Mykolaiv around 5:00. Shelling. A fire broke out in one of the city's districts, and a supermarket was destroyed in another," he said.
Rescue services are working at the scene of the attack. Oleksandr Senkevych promised to provide details later.