Russian state media TASS reported that those on board both vessels were rescued, though one crew member of the Volgoneft 212 is reported to have died.

The tankers were carrying more than 9,000 tons of oil, emergency services reported, according to TASS. Some of this oil spilled into the Kerch Strait, which specialists were preparing to clean up, it said.

The oil spill “has the potential to be serious,” Greenpeace Ukraine said in a statement published on Sunday, especially given the area’s weather conditions, which could make the leak “extremely difficult to contain.”

The impact of the spill could also depend on the type of oil the vessels were carrying, Paul Johnston, head of Greenpeace Research Laboratories, said in the statement. Heavy residual fuel oils would cause more damage than other substances, he said.

The region suffered a similar oil spill in November 2007, when five ships sank in storms in the Black Sea and the Azov Sea.

In that incident, strong winds and high surf caused the Volgoneft 139 to split in two, spilling up 560,000 gallons, or approximately 1,000 tons, of fuel oil.

CNN’s Anna Chernova, Maria Kostenko, Billy Stockwell and Monica Garrett contributed to this report.