A U.S.-flagged oil tanker crashed into a Portuguese-flagged container ship off the coast of the United Kingdom, spilling jet fuel into the North Sea and setting the tanker ablaze.

The crew of the tanker, the Stena Immaculate, abandoned the vessel after multiple explosions on board following the March 10 collision, Crowley ship management said in a statement.  A local politician said one person was hospitalized. The ship was holding about 140,000 barrels of jet fuel at the time, analytics firm Kpler estimates.

The incident is one of the most significant maritime disasters near the U.K. for many years. 

A major support operation is now underway and is being co-ordinated by the local coastguard, according to a separate statement from Stena, which owns the tanker. The incident took place in the North Sea a few miles off the country’s eastern coastline.

Greenpeace U.K. said it was too soon to assess the environmental impact. The extent of any damage will depend on the fuel carried by both ships and how much enters the water. Sea and weather conditions will also play an important role, it said. 

The type of jet fuel that’s leaked isn’t especially flammable though it will burn while floating if the spill is big enough, said Alan Gelder, a senior analyst at consultancy Wood Mackenzie Ltd. If it’s not on fire, the release will disperse through evaporation and wave action that breaks up the spill into small droplets that disperse and are broken down further by biological action, he said.

If confirmed that the Stena Immaculate was carrying 140,000 barrels of jet fuel, and all of it spilled into the sea, that would be about 18,000 tons of petroleum. The biggest global tanker spill in history was 287,000 tons, according to figures from ITOPF data, a nonprofit that provides spill assistance and technical advice for such incidents. 

There have also been significantly larger U.K. spills in the past. In 1967, the supertanker Torrey Canyon ran aground and leaked more than 119,000 tons off the country’s southwest coast.

The Stena Immaculate was awarded a role in the U.S. government’s tanker security program in 2023. Under the program, the vessels continue their international commercial operations, but can be chartered on a short-term basis to serve U.S. government operations. 

The tanker, while at anchor, had an allision — meaning only one of the two was moving at the time — with a container vessel called Solong, Crowley said. Representatives for that freighter didn’t immediately respond to a request for comment.

The U.K.’s Maritime and Coastguard Agency said it was coordinating an emergency response. A rescue helicopter is involved, as well as lifeboats from four stations. The incident is ongoing and an assessment of the pollution response is underway. 

The U.K.’s transport secretary thanked emergency service workers for their efforts responding to the incident.