A growing gas cloud from a leak at a platform operated by Total off Scotland has forced Shell to remove some workers from two nearby rigs for safety reasons.
The gas leak on a rig operated by the French firm began on Sunday and has formed a cloud dense enough to be seen by workers on other North Sea rigs.
Total said it was unable to predict when or how the leak would be contained.
The gas leak at the Elgin well head platform remains ongoing, and we are taking all possible measures to try to identify the source and cause of the leak and to bring it under control, Total UK said in a statement on Monday.
A Total spokesman on Tuesday said company technical teams were investigating the cause of the gas leak but declined to give further details.
The company removed all 238 workers aboard the Elgin rig on Sunday, shutting down oil and gas production and reporting no injuries.
Workers were evacuated to Aberdeen and neighbouring offshore installations.
Shell said it had removed some workers from two of its platforms.
Shell UK Limited can confirm that a partial downman of personnel is underway at the company's Shearwater platform and the nearby Noble Hans Deul drilling rig, a spokesman said.
Both are approximately 225 km (138 miles) east of Aberdeen, with the Shearwater platform about four nautical miles from Total's leaking Elgin rig.
Output from the Shearwater platform was not affected while drilling on Shell's Noble Hans Deul rig was suspended, he said.
Shell considers this to be a prudent precautionary measure following the gas leak, Shell said.
The environmental impact of gas condensate leaks is substantially lower than from oil spills, the UK energy ministry said.
An aerial surveillance flight confirmed there was a sheen on the water. The sheen, thought to be gas condensate, is a direct consequence of the gas leak and usually evaporates naturally, a Total UK spokeswoman said.
The Elgin/Franklin field can produce 280,000 barrels of oil equivalent per day, which includes 175,000 barrels of condensate and 15.5 million cubic metres of gas (mcm/d).
The oil is exported via the BP-operated Forties Pipeline System to Kinneil in Scotland while the gas flows through the SEAL pipeline to Bacton in Norfolk.
Gas flow through the Bacton SEAL terminal fell by around 10 mcm/d to 7 mcm/d early on Monday, data provided by UK energy network operator National Grid showed.
UK gas prices for this week extended gains on Tuesday, rising close to four percent to 57.7 pence per therm.
(Reporting by Oleg Vukmanovic; editing by Jason Neely)