A major rescue operation was being coordinated by the UK Coastguard as images showed a huge plume of thick, black smoke and flames rising from the scene about 10 miles (16 kilometres) off the coast.

The Stena Immaculate was "anchored off the North Sea coast near Hull... (and) was struck by the container ship Solong", the Stena's US-based operators Crowley said in a statement.

The tanker was on a short-term US military charter with Military Sealift Command, according to Jillian Morris, the spokesperson for the command that operates civilian-crewed ships providing ocean transport for the US Defense Department.

Crowley said the impact of the collision "ruptured" the cargo tank "containing A1-jet fuel" and triggered a fire, with fuel "reported released".

A spokesperson for UK Prime Minister Keir Starmer called the situation "extremely concerning".

Grimsby port director Martyn Boyers told AFP that 32 injured people had been brought ashore for treatment in three vessels, adding that "ambulances were queueing on the quay" in the northeastern English fishing port.

Local MP Graham Stuart later wrote on X that 37 people had been injured.

All crew members on board the tanker, owned by Swedish shipowner Stena Bulk, were confirmed to be alive, Lena Alvling, a spokesperson for the firm, told AFP.

- 'Not like crude spill' -

There were reports of "fires on both ships" that UK lifeboat services were responding to, the Royal National Lifeboat Institution (RNLI) confirmed to AFP.

A spokesman said the coastguard was carrying out an assessment of the likely counter-pollution response required, while a government body probing marine accidents deployed a team to Grimsby.

"Our team of inspectors and support staff are gathering evidence and undertaking a preliminary assessment of the accident to determine our next steps," a Marine Accident Investigation Branch spokesperson said.

Ivor Vince, founder of ASK Consultants, an environmental risk advisory group, told AFP that "the good news is it's not persistent, it's not like a crude oil spill".

"Most of it will evaporate quite quickly and what doesn't evaporate will be degraded by microorganisms quite quickly", he added, while warning that "it will kill fish and other creatures".

Martin Slater, director of operations at Yorkshire Wildlife Trust, said it could be potentially "devastating" to seal and bird populations if the nearby Humber estuary became polluted.

- Humber traffic suspended -

All vessel movements were "suspended" in the Humber estuary that flows into the North Sea, according to Associated British Ports (ABP).

The ABP, which operates in the Ports of Hull and Immingham in the region, added that it was "assisting" the Coastguard.

The International Maritime Organization told AFP "the current focus is on the firefighting and search-and-rescue operation".

The alarm about the crash near the port city of Hull in East Yorkshire was raised at 0948 GMT.

A coastguard helicopter, a plane, lifeboats from four towns and other nearby vessels were part of the large rescue operation, UK Coastguard said.

The cargo ship was the Portuguese-flagged "Solong", owned by the German company Reederei Koepping.

The 140-metre-long (460 foot) cargo vessel left Grangemouth in Scotland and was bound for Rotterdam, according to the Vessel Finder website.

- Collisions rare -

Vessels with firefighting capabilities have been dispatched to the scene off the northeast coast.

Collisions remain rare in the busy North Sea.

In October 2023, two cargo ships, the Verity and the Polesie, collided near Germany's Heligoland islands in the North Sea.

Three people were killed and two others are still missing and considered dead.

The Isle-of-Man-flagged Verity, which was carrying steel from the northern German port of Bremen to Immingham, sank.

In October 2015, the Flinterstar freighter, carrying 125 tonnes of diesel and 427 tonnes of fuel oil, sank after colliding with the Al Oraiq tanker eight kilometres (five miles) off the Belgian coast.

A major North Sea oil spill took place in January 1993 when the Liberian tanker Braer suffered engine damage while en route to Canada from Norway.

Water seeped into the holds of the ship, which ran aground off Scotland's Shetland Islands and released 84,500 tonnes of crude oil.