Ukraine and Russia have both reportedly carried out night attacks on ports.
A missile attack by Ukraine caused a large fire in Sevastopol, Crimea, injuring 24 people, Russian-installed governor Mikhail Razvozhayev said.
Mr Razvozhayev said the attack had hit a shipyard in the port city, home to Russia`s Black Sea Fleet.
And Russian drones reportedly damaged the Ukrainian grain port of Izmail, on the Danube river.
The governor of the Odesa region, Oleh Kiper, said six people had been injured in the attack, which caused a fire and damaged infrastructure.
"Several groups of drones were launched at the Izmail district," Mr Kiper said on Telegram. "Unfortunately, there were hits: damage to port and other civil infrastructure was recorded."
Mr Razvozhayev said emergency services were at the scene of the blaze in Sevastopol. "There is no danger to civilian installations in the city," he added.
A photo shared by Mr Razvozhayev on Telegram shows flames engulfing what appears to be vessel at a port as he stands speaking into his phone.