Grimsby, United Kingdom –

British police on Tuesday arrested on suspicion of manslaughter the captain of a ship that crashed into a tanker in the North Sea, sparking a massive blaze and leaving one crew member missing, presumed dead.

Investigations have already started into what led the cargo ship to strike the tanker carrying jet fuel on Monday, as fears remained of possible harm to the area's marine and wildlife.

The U.K. Coastguard, which led the operation, rescued 36 people on Monday, including all of the 23 crew on the U.S.-flagged Stena Immaculate tanker, which had been chartered by the U.S. military.

But a missing member of the Solong cargo vessel crew was "likely deceased," U.K. Under Secretary for Transport Mike Kane told Parliament.

Humberside Police in northeastern England said they had arrested a 59-year-old man on suspicion of gross negligence manslaughter in connection with the collision.

Ernst Russ, owner of the cargo ship, then issued a statement saying that it "can confirm that the master of the ... Solong has been detained by Humberside police in the U.K.."

"The master and our entire team are actively assisting with the investigations," it added.

Kane said the fire on the Stena Immaculate "appears to be extinguished" but this was not immediately confirmed by the coast guard.

"The Solong is still alight and the fire on board the Stena Immaculate has greatly diminished," the U.K. Coastguard said.

The coast guard was closely monitoring the Solong, which had broken free of the tanker overnight and was limping southward, accompanied by four tug boats, including one that had a line attached to the stricken vessel.

Transport Secretary Heidi Alexander said she met the Maritime and Coastguard Agency's chief executive, Virginia McVea, on Tuesday and was "pleased to have been informed that early indications suggest that both vessels are now expected to stay afloat."

Photos taken during a helicopter flyover showed smoke still pouring from the Solong, while a large hole could be seen in the side of the Stena Immaculate.

The accident occurred at around 0948 GMT on Monday when the Portuguese-flagged cargo ship plowed into the tanker, anchored about 21 kilometers off the northeastern port of Hull.

According to data collected by website VesselFinder, the collision displaced the tanker by "more than 400 meters."

The Stena Immaculate was on a short-term U.S. military charter with Military Sealift Command, according to a spokesperson for the command, which operates civilian-crewed ships for the U.S. Defense Department.

Crowley, the U.S.-based operator of the Stena Immaculate, said the crash had "ruptured" the tank "containing A1-jet fuel" and triggered a fire, with fuel "reported released."

There was "no evidence of foul play," Kane said in his statement to parliament.

The Stena Immaculate was carrying around 220,000 barrels of jet fuel, Crowley confirmed.

The German owners of the Solong on Tuesday, however, said that the container ship was not carrying sodium cyanide, as had been reported the previous day.

"We are able to confirm that there are no containers on board with sodium cyanide (inside)," Ernst Russ said.

Kane said that "no signs of pollution from vessels is observed at this time," but that the situation was being monitored.

Dutch maritime servicing company Boskalis told the Netherlands' ANP news agency it had been tasked with salvaging the Stena Immaculate and was also measuring the atmosphere around the vessel for potential toxic fumes.

U.K. Housing Minister Matthew Pennycook said the investigation was being led by U.S. and Portuguese authorities, since the vessels were sailing under their flags.

"We're obviously very alive to the potential impact on the environment," he told Times Radio, but added that the coast guard was well equipped to deal with any oil spills.

Paul Johnston, a senior scientist at the Greenpeace Research Laboratories at Exeter University, said: "We are extremely concerned about the multiple toxic hazards."

There are several nature reserves along the Humber estuary.

"The good news is it's not like a crude oil spill," Ivor Vince, founder of environmental risk advisory group ASK Consultants, said.

"Most of it will evaporate quite quickly and what doesn't evaporate will be degraded by microorganisms quite quickly," he said.

His Majesty's Coastguard on Tuesday said that the threat from dangerous goods on board has "reduced significantly" and that air quality sampling onshore had shown no toxins, while modelling from the Met Office indicated "no threat to the public."