The explosion occurred a few meters from the shore where people were swimming in Odessa. This was reported by the Ukrainian publication Strana, citing posts on social networks.
Eyewitnesses suggest it could be a mine.
At 08:15 an air raid alert was issued over the Odessa region; it lasted about 15 minutes. At 08:48 the air distress signal was heard again in the region.
The news is being updated.