A two-mile exclusion zone has been set up around an offshore platform which has been evacuated after a gas leak.
The leak on Total's Elgin PUQ platform, about 150 miles (241km) off the coast of Aberdeen, led to the evacuation of all 238 workers on Sunday.
Total have admitted it could be six months before a relief well to stop the leak is in place.
Yesterday, Shell reduced its workforce on two offshore installations close to the Elgin platform.
Around 85 staff have been taken off the company's Shearwater platform and the nearby Noble Hans Deul drilling rig, leaving a workforce of 117 people.
Aberdeen Coastguard said an exclusion zone of two nautical miles (2.3 miles) around Elgin has been set up, with ships and aircraft ordered to stay away from the area.
Total E&P UK (TEP UK), which operates the platform, said it was taking "all possible measures" to try to identify the source and cause of the leak and to bring it under control.
It has been confirmed that there is a sheen on the water near the platform.
David Hainsworth, health, safety and environment manager for Total, told the Good Morning Scotland programme that there are risks around the situation.
He said: "The gas is flammable but the platform power was turned off to minimise risk of ignition, but clearly there is a risk.
"We have taken away a series of risks but there is always a possibility, it's low but you never say never. The best-case scenario is that the gas in this area is not very productive and it dies off in the coming days and weeks.
He added: "At the moment there is no real evolution of the sheen on the sea but if that was to change ... then the exclusion zone may be increased."
Vicky Wyatt, senior energy campaigner for Greenpeace, said:
“The gas leak on the Total platform off the coast of Aberdeen is a reminder of the dangers that drilling for oil and gas pose to the lives of those working on rigs, and the huge damage that can be done to the environment.
“This leak also shows how reckless George Osborne was to hand over billions of pounds of taxpayers’ money to the oil and gas industry just last week to subsidise deep water drilling to the west of Shetland."
Oil Spill Response (OSRL) carried out two aerial surveillance flights yesterday to assess the situation and two further flights are planned today.
The Shell platform is around four nautical miles (4.6 miles) from the Elgin platform.
Drilling operations on the Noble Hans Deul rig have been suspended and the wells have been left in a safe state, Shell said.
A Shell spokesman said: "While the move is purely precautionary and primarily driven by the prevailing weather conditions, and both facilities remain operational, it has been decided to reduce numbers to a more manageable level until the full situation surrounding the Elgin leak has been established."
Following the discovery of the leak on Sunday, 219 staff were evacuated from the Elgin platform and the nearby Rowan Viking drilling rig.
Nineteen core crew were initially left on board but were taken off overnight between Sunday and Monday and flown to Aberdeen. There have been no reports of any injuries.
Aberdeen Coastguard co-ordinated the evacuation of the Elgin platform.
Coastguard watch manager Kevin Brown said three rescue helicopters and four civilian helicopters helped with the process.
TEP UK said it met the Secretary of State's representative, the Health and Safety Executive, the Department of Energy and Climate change, Marine Scotland and the Coastguard yesterday.
The company said it has also mobilised experts from elsewhere in the Total Group to offer additional assistance and help deal with the incident.
In a statement, the company said: "Total E&P UK confirms that the gas leak at the Elgin Well Head Platform remains ongoing, although the situation is currently stable.
"We continue to take all possible measures to try to identify the source and cause of the leak and to bring it under control."