A Russian oil tanker has split in half during a severe storm near the Black Sea, spilling around 1,300 tonnes of fuel oil.
A Russian official said it was a “very serious environmental disaster”, which would take years to solve.
The vessel was at the Kerch Strait, between the Azov and Black Seas, when it broke up after being battered by 5m (16.5ft) high waves on Sunday morning.
Efforts to rescue the 13 crew are being hampered by harsh weather conditions.
The oil tanker, reportedly owned by Russian firm Volganeft, was at anchor when its stern and rear tore apart in the storm, officials said.
“This problem may take a few years to solve. Fuel oil is a heavy substance and it is now sinking to the seabed,” said an official from Russia’s state environmental protection agency Rosprirodnadzor.
“This is a very serious environmental disaster,” Reuters quoted him as telling Russia’s state-run Vesti-24 channel.
But the spill is small by comparison with the Prestige disaster off Spain five years ago.
Severe habitat damage was caused to beaches in Spain, France and Portugal when a tanker leaked 64,000 tonnes of fuel oil in November 2002.
Sunday’s accident happened in the waters of Ukraine at the strait which divides that country and Russia.
The tanker was carrying fuel oil from the southern Russian city of Samara on the Volga River to a port in Ukraine.
Another cargo ship carrying 2,000 tonnes of sulphur sank nearby and its nine crew members were rescued.