Keith Churchman, of Harwich Royal National Lifeboat Institution, said: “The damage is very extensive. The fire started in a generator and spread quickly to the accommodation.
“There have been a number of explosions on board as the fire has engulfed gas bottles and batteries. Only one person was on Sealand at the time, whom we understand to be a watchman whose job was to maintain the generators and equipment.“
A team of firefighters was flown to the scene but because of the damage to the structure they decided not to go on board.“A firefighting tug sprayed the whole structure with water in the hope this would eventually cool the fire and starve it of oxygen.”
A spokesperson for Suffolk Fire Service confirmed the fire was left to burn itself out and was under control by 3.10pm.