At least 10 people are dead after two Tanzanian-flagged ships caught fire Monday in the Kerch Strait off the coast of Russian-annexed Crimea.
Russian authorities said at least 12 people were rescued, but the rest are missing.
The ships, the Kandy and the Maestro, had crews that were nationals from India and Turkey. Together, the two ships carried 31 crew members.
Russia's transport ministry said a rescue operation was under way to find sailors who jumped overboard to escape the blaze, which ignited when fuel was being transferred from one ship to another.
Ships in 'neutral water'
The crew members were sailing in "neutral waters" in the Black Sea when the incident occurred, authorities said.
The Kerch Strait is a point of high tension between Russia and Ukraine.
In November, Russia fired on and seized three Ukrainian navy ships in the strait as they tried to pass from the Black Sea to the Azov Sea. Russia continues to hold 24 Ukrainian sailors captured in the incident. They are accused of illegally crossing into Russian territory.
Ukraine has denied the accusation.