"As more information emerges about what the ships were carrying, we are extremely concerned about the multiple toxic hazards these chemicals could pose to marine life," said Paul Johnston, a senior scientist at the Greenpeace Research Laboratories at Exeter University.

"The jet fuel that entered the water close to a breeding ground for harbour porpoises is toxic to fish and other sea creatures," he added.

Monday's collision, in which the container vessel Solong hit the tanker Stena Immaculate while it was anchored about 10 miles (16 kilometres) off the coast of Hull, has set off a major pollution alert on the northeastern English coast.

Business information service Lloyd's List Intelligence said it understood that the Stena Immaculate was carrying around 220,000 barrels of jet fuel.

"The containership was carrying an unknown quantity of alcohol and 15 containers of sodium cyanide," Lloyd's List intelligence added.

Tom Webb, senior lecturer in marine ecology and conservation at the University of Sheffield, said the area was known for its rich wildlife including wading birds and waterfowl.

"Chemical pollution resulting from incidents of this kind can directly impact birds, and it can also have long-lasting effects on the marine food webs that support them," he said.