A tanker carrying jet fuel was ablaze and leaking in the North Sea off northeast England after a collision with a cargo vessel, with more than 30 crew sent to hospital.

The coastguard agency said a helicopter, fixed-wing aircraft, lifeboats and nearby vessels with firefighting capability had all been called to the incident to help.

The tanker, which can carry tens of thousands of tons of jet fuel, was at anchor when the smaller container ship struck it, rupturing its cargo tank and releasing fuel into the sea, its operator said. Its owner Stena Bulk gave the same details.

Two maritime security sources said there was no indication of any malicious activity or other actors involved in the incident.

Britain's coastguard said in a statement that 36 crew members were taken safely ashore, with one person hospitalized.

The coastguard said one crew member of the Portuguese-flagged cargo ship Solong remained missing and the search has ended.

Ambulances carrying casualties leave port after tanker collision off UK coast. – Reuters

Thirty-two casualties were brought ashore with ambulances waiting to take them to hospital in Grimsby, the chief executive of the Port of Grimsby East said via email. It was not clear how severe their condition was.

The vessels involved are the U.S.-flagged 49,729 deadweight tonnage (dwt) tanker Stena Immaculate and the Portuguese-flagged 9,322 dwt container ship Solong. The tanker is one of 10 in a U.S. government programme designed to supply the armed forces with fuel when required.

Television images from the BBC showed at least one vessel ablaze with clouds of black smoke billowing into a grey sky.

The Stena Immaculate and Solong were alongside each other off the coast, according to the last AIS ship tracking position update at 1034 GMT, LSEG shipping data showed.

Stena said its tanker was operated by U.S. logistics group Crowley. Crowley wrote on X that the tanker, carrying a cargo of Jet-A1 fuel, was struck by the Solong while anchored near Hull off the North Sea coast.

"The Stena Immaculate sustained a ruptured cargo tank," Crowley said.

"A fire occurred as a result of the allision and fuel was reported released," the company said, referring to when one vessel is stationary.

The crew of the Stena Immaculate abandoned the vessel following multiple explosions onboard and all mariners were safe and accounted for, Crowley said.

"The Stena vessel is a products tanker. Pollution risk less than if it were a crude carrier," one insurance specialist said.

"A lot depends really on cargo carried, how many tanks were breached and how bad the fire is."

It was too early to assess the extent of any environmental damage, a spokesperson with environmental group Greenpeace said.

"The magnitude of any impact will depend on a number of factors, including the amount and type of oil carried by the tanker, the fuel carried by both ships, and how much of that, if any, has entered the water," the Greenpeace spokesperson said.

"Sea and weather conditions will also be important in determining how any spill behaves."

Tracker shows tanker involved in collision off northeast coast. – Reuters

The incident occurred in a busy stretch of waterway, with traffic running from the ports along Britain's northeast coast to the Netherlands and Germany, shipping industry sources said.

The Royal National Lifeboat Institution (RNLI), a lifeboat service working on the emergency response, said:

"There were reports that a number of people had abandoned the vessels following a collision and there were fires on both ships."

Maritime analytics website Marine Traffic said the 183-metre-long Stena Immaculate was anchored off Immingham, northeast England, when it was struck by the 140-metre-long Solong, which was en route to Rotterdam.

Ship insurer Skuld of Norway would only confirm that the Solong was covered with it for protection & indemnity (P&I), a segment of insurance that covers environmental damage and crew injuries or fatalities.

Solong's manager, Hamburg-based Ernst Russ, did not immediately respond to a request for comment. Stena Immaculate's P&I insurer, which was listed as Steamship, did not immediately respond to a request for comment.

The United Nations shipping agency, the International Maritime Organization, said it was aware of the situation.