A thick cloud of gas now hangs over the top of the Elgin-Franklin hub which witnesses say can be seen for miles.
Beneath the cloud, a 23.5-tonne sheen of hydrocarbons is reportedly “boiling” on the sea surface.
As a precaution, all flights overhead have now been banned and vessels are forbidden from coming within two miles of the abandoned rig in fear of it exploding.
Owner Total has confirmed the leak is continuing and investigations by multiple organisations are under way to assess the health, safety and environmental impacts the latest North Sea gas leak will have.
Members from Oil Spill Response (OSRL) carried out two aerial surveillance flights yesterday to assess the situation. Initial reports indicated there has been no change in the size or appearance of the sheen throughout the course of the day. To evaluate the full environmental extent of the situation, the oil company has ordered three surveillance flights to be carried out each day until the leak is stopped.
Industry union leader Jake Molloy said he was concerned the leak may have similar consequences to those experienced on the Deepwater Horizon.
He said: “It appears, from what I have been told thus far, that the standby vessel which circles the installation had actually seen gas on the surface of the sea. Apparently the sea was seen to be boiling with gas below the rig, which suggests a subsea problem.
“We still have Deepwater Horizon in the forefront of our minds. That was also a gas leak and subsequently an explosion.”
Deepwater Horizon, in the Gulf of Mexico, went down in April 2010, after an explosion on the rig caused by a blowout, killing 11 crewmen and igniting a fireball visible from 35 miles away. It caused the largest offshore oil spill in US history.
The Elgin leak has occurred on the installation above the waterline and last night Total was unable to confirm if there was another leak below the waves.
Mr Molloy added: “If the planes are going out to Elgin that would verify, I would say, they have got a subsea problem and they anticipate the escape of oil into the sea.”
Environment Minister Richard Lochhead said last night that Scottish ministers were treating it as a “serious incident”.
He said: “While governmental responsibility for health and safety in our offshore industry is currently reserved to the UK Department for Energy and Climate change at Westminster, Scottish ministers are fully aware of the situation and we are being kept fully informed of developments.
“We will support work to manage the incident and the thorough and robust investigation that will follow.”
Yesterday, Total started work to try to minimise the environmental damage caused by the leak.
Bosses from the oil company met with Secretary of State’s Representative (SOSREP), the Health and Safety Executive, the Department of Energy and Climate Change (DECC), Marine Scotland and the Coastguard – which led the initial evacuation.
SOSREP has taken the decision not to activate their Operations Control Unit, leaving “primacy” of the incident with Total.