Here is what we know about the incident involving the tanker Stena Immaculate and the container vessel Solong, which set off a major pollution alert on England's east coast.

- Tanker at anchor -

The Stena Immaculate was carrying 220,000 barrels of the fuel, according to the maritime information service, Lloyd's List Intelligence.

It was at anchor about 10 miles (16 kilometres) off the northeastern England port of Hull when it was "struck by the container ship Solong", said Crowley Maritime, the US shipping firm managing the tanker.

The alarm was raised at 0948 GMT.

Lloyd's List said the Solong was carrying 15 containers of sodium cyanide.

But UK authorities have not confirmed the presence of the compound, which releases flammable gas on contact with water. It is also not confirmed if any had leaked.

A massive fire erupted and engulfed both vessels.

Crowley Maritime said the tanker was carrying jet-A1 fuel and the US Defense Department has confirmed that the US military had chartered the vessel.

The tanker "crew abandoned the vessel following multiple explosions onboard" said Crowley Maritime, which is based in Jacksonville, Florida.

The UK Coastguard said 36 people had been rescued, with one taken to hospital.

Stena Bulk, a Swedish company that owns the tanker, said all of the crew on the vessel were alive.

Thirteen of the Solong's 14 crew members were brought ashore, said the ship's German-based owner Ernst Russ. The search for the missing crew member was called off late on Monday.

The Coastguard said the search had now "ended".

- Ships ablaze -

Latest images on the BBC showed a large hole in the side the tanker and a huge plume of thick black smoke rising from the ships.

Both stationary vessels were surrounded by smaller ships dousing the fire.

The UK Coastguard was coordinating the emergency pollution operation after Crowley Maritime said the impact had "ruptured" the tanker and set off the fire.

Following initial efforts to extinguish the blaze, four further ships with firefighting capacity were on their way to the site, according to Dutch maritime servicing company Boskalis, tasked with salvaging the Stena.

The tanker would need to be "cooled down" before the fire could be put out, it said.

The government Marine Accident Investigation Branch said it had a team at the scene already "gathering evidence" and assessing "next steps".

The investigation was being led by the US and Portuguese authorities, as the ships were flagged from their countries, UK housing minister Matthew Pennycook said.

- Traffic suspended -

Associated British Ports (ABP), which operates ports in Hull and Immingham, the stricken region, said it had halted all vessel movements in the Humber estuary that flows into the North Sea.

- Relatively rare -

The North Sea has busy shipping lanes but accidents are relatively rare.

In October 2023, two cargo ships, the Verity and the Polesie, collided near Germany's Heligoland islands. Three people were killed and two others were listed as missing.

On October 6 2015, the freighter Flinterstar, carrying 125 tonnes of diesel and 427 tonnes of fuel oil, sank after colliding with the tanker Al Oraiq eight kilometres (five miles) off the Belgian coast.

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

It ran aground off Scotland's Shetland Islands and released 84,500 tonnes of crude oil.

- Proper lookout? -

David McFarlane of the Maritime Risk and Safety consultancy said there were 200 to 300 ship collisions around the world each year, but most are just a "slight bump" in port.

"The collision regulations... state that all ships must maintain a proper lookout at all times. And clearly something has gone wrong here, because if a proper lookout had been maintained, this collision would have been avoided," McFarlane told AFP.

When the flames die down investigators will look for the video data recorders on the two ships -- the equivalent of a plane's "black box" data recorders.

These should have information from the ships' radar as well as voice recordings of the bridge teams. McFarlane said this would help investigators find out if there was communication between the two ships.

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