Total is still evaluating ways to solve a gas leak on a North Sea platform and has dispatched fire-fighting ships near the scene in case of an explosion, a spokesman for the French oil company said on Thursday.

A flare needed to purge any gas left in the platform is burning less than 100 metres from where explosive natural gas is still leaking.

The spokesman said the flare should extinguish naturally in the next few days.

Total has not yet found a way to stop the above-water gas leak which started on Sunday and forced the evacuation of all 238 workers from the platform, which sits 240 km (150 miles) off the east coast of Scotland.

The leak is on the deck level of the well head platform.

We are still evaluating solutions, the spokesman said, adding it would take days before decisions were made. We have sent fire-fighting boats outside the security zone.

An exclusion zone has been set up around the leaking Elgin platform, with ships ordered to come no closer than two miles and aircraft no nearer than three miles if they fly lower than 4,000 feet.

The firm as well as UK authorities have said the expected environmental impact from the plume of gas and a spreading sheen of light oil on the water would be minimal, although environmental pollution experts said much of the gas cocktail would be either flammable or poisonous at close quarters.

Total could face costs of up to $10 billion (6 billion pounds) if its North Sea gas leak leads to an explosion and nearly $3 billion if it takes months to fix, according to analysts' early estimates.

Following BP's Gulf of Mexico oil disaster in 2010, the British company was forced to make provisions of over $32 billion and suffered damage to its corporate reputation.

Total's shares have lost about 9 percent in the wake of the incident. They were trading at 37.13 euros, off 2.34 percent, at 1037 GMT.

(Reporting by Muriel Boselli; editing by Jason Neely)