The leaking Elgin platform was last night labelled “the well from hell” by one environmentalist.
The gas cloud which has engulfed the field can be seen from other oil platforms and support vessels miles away.
Beneath the cloud, a 23.5-tonne sheen of hydrocarbons is reportedly “boiling” on the sea surface.
Last night, a spokesman for Aberdeen Coastguard said the cloud was travelling in a north-easterly direction, which has led to a halt in production at Shell’s nearby Shearwater platform.
Environmentalists have warned the Elgin problem will only get “bigger and bigger”.
Frederic Hauge, of Norwegian oil consultant Bellona, said: “This is the well from hell. The problem is out of control.
“They saw the sea bubbling with gas under the platform. This is quite shocking.”
Jake Molloy, regional organiser for the RMT union, said he was concerned the leak may have similar consequences to those experienced on BP’s Deepwater Horizon.
He said: “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 collapsed into the sea 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 led to the largest offshore oil spill in US history.
David Hainsworth, health, safety and environmental manager at Total said the sheen had reduced in size since initial measurements were taken on Sunday.
he added: “It is very difficult to calculate how much gas has been released but if we had to give a figure we would say around two kilograms of gas is being released every second.”