Authorities estimate the tankers were carrying 9,200 tons of fuel oil, of which approximately 40% potentially leaked into the sea. Kremlin spokesperson Dmitry Peskov described the situation as "truly critical.

The Russian government made the declaration after a number of its tankers were sank in the body of water between itself, Ukraine, Turkey and Romania.

A regional state of emergency was introduced in the occupied Crimea. The reason was a fuel oil spill in the Black Sea, according to the Russian media. The corresponding decree was issued by the Governor of Crimea Sergey Aksyonov.

Authorities in Russia's southern Krasnodar region on Wednesday declared a region-wide emergency, saying that oil was still washing up on the coastline 10 days after two ageing tankers ran into trouble.

One tanker sank and another ran aground on December 15 in the Kerch Strait between Russia and the annexed Crimean peninsula.

Russian ruler Vladimir Putin has introduced a federal state of emergency due to the fuel oil spill following the 15 December tanker accident in the Kerch Strait. Source: Latvia-based Russian media outlet Meduza;

Volunteers helping to clean up a major oil spill along Russia's Black Sea coast appealed in a video released on Monday for President Vladimir Putin to urgently send federal aid, saying that they and local authorities were overwhelmed.

Russia Wednesday expanded an operation to clean up thousands of tonnes of oil that spilt into the sea and contaminated 50 kilometers of beaches after tanker ships were wrecked in a storm.