A dramatic collision in the North Sea has set ablaze an oil tanker and a cargo ship, raising fears of an environmental disaster.

On Monday, the US-flagged oil tanker MV Stena Immaculate collided with the Portuguese cargo ship MV Solong. The crash started a huge fire, which is still burning in the North Sea, about 10 miles (16km) off the coast of the busy Hull port and fishing centre.

Dozens of people were rescued, but one crew member who remained unaccounted for, is presumed dead. A 59-year-old man who, according to the ship’s owners, is the captain of the Solong, was arrested on suspicion of gross negligence manslaughter.

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The Stena Immaculate was transporting Jet A-1 aviation fuel intended for military use. Initial reports suggested that the Solong was carrying 15 containers of sodium cyanide – a highly toxic substance – raising fears of a hazardous chemical spill.

However, Ernst Russ, the shipping firm that owns the vessel, has since confirmed that no sodium cyanide was on board, easing concerns over a toxic leak.

Experts warn a fuel spill could impact marine life, seabirds, and fragile ecosystems in and around the Humber Estuary.

The alarm was first raised on the Humber Estuary in East Yorkshire at 9.48am on Monday. A Portuguese-flagged cargo vessel collided with a US-flagged oil tanker, which was understood to be at anchor and carrying aviation fuel.

A mayday call from the HM Coastguard requested help from vessels with fire-fighting equipment or which could assist with search and rescue.

The collision took place on the Humber Estuary in East Yorkshire, with the oil tanker at anchor.

Martyn Boyers, chief executive of the Port of Grimsby East, said he had been told there was “a massive fireball” following the crash.

It’s unclear what led to the collision, but Dr Seyedvahid Vakili, a maritime expert at the University of Southampton says “in most cases human factors play a significant role”.

“This is particularly relevant for container vessels where high workloads and fatigue can be major contributing factors.”

In an update late on Monday, Crowley, who manages the oil tanker, said at least one cargo tank carrying A1-jet fuel was ruptured in the collision.

A spokesperson said: “At this stage, it is unclear what volume of fuel may have been released as a result of the incident. At the time it was struck, the 183m (596ft) Stena Immaculate was carrying 220,000 barrels of jet fuel in 16 segregated cargo tanks.

“Crowley is supporting the relevant authorities in the UK who are investigating the incident and will defer to them for any further questions on potential cause.”

“From an aquatic environment perspective, jet fuel evaporates faster and is less concerning than crude oil. But immediate acute impacts on marine organisms will still be severe,” Dr Mark Hartl, marine ecotoxicologist at Heriot-Watt University, said.

Professor Tiago Alves from the Cardiff University said conditions in the North Sea might mitigate some impacts.

“Environmentally, jet fuel evaporates easily and combusts quickly. Impacts may be felt mostly near the accident site, especially given today’s windy conditions and dynamic wave energy which favour dispersion,” prof Alves said.

However, Alastair Grant, Emeritus Professor of Ecology at the University of East Anglia, said jet fuel “contains up to 25 per cent aromatic hydrocarbons, which are relatively toxic and slow to break down in the environment. This makes it approximately 50 times more toxic to aquatic life than diesel oil, and significantly more harmful than crude oil”.

The situation is further complicated by concerns over heavier bunker fuels used by ships, scientists warn.

“This particular incident is troubling because it appears to involve persistent oil, which breaks up slowly in water,” Dr Alex Lukyanov, researcher at the University of Reading, said.

“Persistent oils like marine diesel can smother habitats and wildlife, affecting their ability to regulate body temperature, potentially resulting in death.”

The collision occurred close to critical marine habitats at a sensitive time for wildlife. There are several Marine protected areas near Hull such as Flamborough Hea and Holderness. These areas are protected due to their rich habitats supporting marine wildlife including fish, bivalves, crabs and birds

“Around Flamborough the nesting season will soon start,” Dr Daniela Schmidt, professor of earth sciences at University of Bristol, said.

“While the first focus is on containing the fire, the pollution connected to the accident has the potential to spread widely depending on the currents and waves with the risk of impacting these protected areas.”

Martin Slater of the Yorkshire Wildlife Trust warned pollution could be “devastating” for seabirds, grey seals, and cetaceans near Spurn, as many birds gather offshore for nesting season.

Calum Duncan of the Marine Conservation Society explained that the biggest challenge now is containment. And how far the leak would spread depends on several environmental factors.

How far and fast any pollution spreads depends greatly on weather and sea conditions.

“Forecasting the environmental of oil spills is extremely complex. Oil spills like the one in the North Sea are affected by multiple factors. The size of the spill, weather conditions, sea currents, water waves, wind patterns, and the type of oil involved all play crucial roles in determining environmental outcomes,” Dr Alex Lukyanov from the University of Reading said.

“Persistent oils like marine diesel are particularly troubling because they linger, smothering habitats and wildlife over long periods.”

The fierce fires burning aboard the ships are also releasing thick clouds of toxic black smoke, raising concerns over air quality and health impacts for coastal communities. Meanwhile, any spilled cargo could mean plastics and debris washing ashore for years, harming marine wildlife far into the future.

Scientists are looking at past incidents, such as the 1993 MV Braer spill off the Shetland Isles, for insight.

Investigations are now being led by authorities from the United States and Portugal to determine the cause and extent of the environmental impact. The full environmental consequences may not be fully understood for months.