About 1,300 tons of fuel oil have leaked near the Black Sea after a Russian oil tanker split in half - in a storm that sank three other ships.

A Russian official said the tanker accident was a "very serious environmental disaster".

The vessel came apart after it was smashed by 5m (16ft) waves at the Kerch Strait between the Azov and Black Seas.

The weather is hampering efforts to rescue its 13 crew, as well as up to 10 sailors missing from two other ships.

Dozens of vessels have reportedly been evacuated from the busy Russian commercial port of Kavkaz because of the storm, which was packing winds of 108km/h (67 mph).

'Sinking to seabed'

The broken oil tanker, reportedly owned by Russian firm Volganeft, was at anchor when its stern tore apart in the waters of Ukraine at the busy waterway dividing that country and Russia, 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 oil 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.

The two other vessels that sank in Sunday's storm were carrying up to 2,000 tonnes of sulphur each, with eight sailors missing from one of the freighters.

Meanwhile, several crew members were reportedly missing from a scrap metal ship that sank 300km (187 miles) further west, near Sevastopol on Ukraine's Crimean Peninsula.

PHOTO CAPTION

A map shows the black sea