A severe storm broke a Russian oil tanker in two, spilling fuel oil into the sea in what a Russian official said was an "environmental disaster".
The tanker, Volganeft-139, was on its way from the port of Azov in the southern Russian region of Rostov to Kerch in Ukraine's eastern Crimea when high waves broke its hull overnight.
The tanker's 13 crew members drifted for hours aboard the ship's stern in waves up to 6 metres high before beaching safely a few miles from the bow section.
The tanker was carrying 4,000 tonnes of fuel oil in total, officials were quoted by media as saying.
"According to preliminary data, some 1,300 tonnes of fuel oil could have spilt into the sea," Russia's state-run Vesti-24 channel quoted emergencies ministry officials saying.
But Oleg Mitvol, deputy head of the environmnetal protection agency, Rosprirodnadzor, said the as much as 2,000 tonnes had leaked.
"This problem may take a few years to solve. Fuel oil is a heavy substance and it is now sinking to the seabed," Mr Mitvol said.
"This is a very serious environmental disaster."
The likely effects of the spill were not immediately clear. When the oil tanker Prestige sank off Spain in November 2002, about 64,000 tonnes of fuel oil leaked, causing severe habitat damage to beaches in France, Spain and Portugal.
Almost at the same time as the Volganeft-139broke up, a freighter carrying 2,000 tonnes of sulphur sank in the same storm, off the port of Kavkaz overlooking the Kerch Strait from the Russian side.
Its crew of eight had been rescued after drifting in a raft for a few hours. "Sulphur is a very inert chemical, and we hope that in the water it will not form any substances dangerous to humans," Mr Mitvol said.
As he spoke, news came of another oil tanker, Volganeft-123, the hull of which cracked after being hit by high waves.
Maxim Stepanenko, transport prosecutor of the nearby Russian Black Sea port of Novorossiisk, told Russian television this tanker was afloat and its oil products were not leaking.