Total said it was looking at ways to extinguish a flare left burning less than 100 metres from where explosive natural gas was leaking from the French energy company's Elgin North Sea platform for a fifth day.

Total dismissed the risk of a blast at the platform, 240 km (150 miles) off the east coast of Scotland, and the British government said the flame had to remain burning to prevent excess gas pressure from building up.

But one energy industry consultant said Elgin could become an explosion waiting to happen if the oil major did not rapidly stop the leak which is above the water at the wellhead.

Total's share price dropped about 7 percent on Tuesday and Wednesday, though some analysts said the leak did not appear to be as serious as the oil leak that caused BP's Deepwater Horizon disaster in 2010, the world's worst marine oil spill.

A spokesman for Total UK said the flare was on a separate platform from the leak, albeit only a short distance away.

The flare is still burning but is not posing a risk. The leak is on the wellhead platform and the flare is on the Processing, Utilities and Quarters platform. There is a gap of 90 metres (300 feet) between the two, he said.

Total said it expected the flare to exhaust itself and burn out. The company was looking at ways to extinguish the flare if this did not happen.

David Hainsworth, a health, safety and environment manager at Total, told the BBC the priority had been the safety of the 238 staff of the platform when it was evacuated on Sunday.

Memories are still raw in the North Sea industry of the Piper Alpha platform fire 24 years ago, when 167 people were killed in the world's deadliest offshore oil disaster.

Hainsworth could not say how long it would take to extinguish the flame, and whether that would be an hour, or 24 hours or two days - or even longer.

The British government said the flame was still alight as part of the safety system triggered during the evacuation to burn off excess gas.

At the moment wind is taking the gas cloud away from the flame and weather conditions are forecast to remain stable for the next few days, said a spokesman for the Department of Energy and Climate Change. We hope that the pressure will be such that the flame will naturally go out by itself, but Total are not taking that for granted.

UNWELCOME NEWS

Industry consultant John Shanks said the stakes were high for the offshore industry. The news this morning that the flare is still burning on the platform is thus unwelcome, said Shanks, who works at RiserTec, a specialist engineering consultancy based in Aberdeen.

Under normal conditions, the deeper the leak, the more difficult remedial work will be. However, if gas continues to leak at a steady or increased rate over a sustained period of time, the platform could become an explosion waiting to happen.

A spokesman for Total in Paris said a solution to plugging the leak was still being evaluated and it was a question of days. We have not precisely identified the cause of the incident, he said.

The British energy ministry said Total was considering two options to plug the leak: drilling a relief well that would allow the flow of gas to be shut off, or blocking the well with heavy mud.

Total warned on Tuesday that it could take six months to halt the flow of gas in an accident that has thrown a spotlight on the safety record of energy production in the British sector of the North Sea.

Hainsworth said then that some weeks ago Total engineers had decided to pump mud into redundant piping on a gas reservoir which had been plugged about a year ago. This appeared to result in the escape of gas from the outer casing of the well.

Credit ratings agency Fitch said current reports of the leak suggested the incident was not as serious as the explosion at the Deepwater Horizon platform in the Gulf of Mexico.

That blast killed 11 workers and ruptured BP's Macondo well, unleashing millions of barrels of oil into the Gulf of Mexico. BP struck a deal estimated at $7.8 billion with businesses and individuals suing over the spill.

Analysts' estimates of the costs to Total of the Elgin leak ranged from $150 million to $2.7 billion, depending on how long the company takes to bring it under control.

In the worst-case scenario of an explosion on the platform, however, the cost could soar to at least $10 billion, not including possible environmental fines, they said.

(Additional reporting by Muriel Boselli, Valerie Parent and Blaise Robinson in Paris, Henning Gloystein, Oleg Vukmanovic, Sarah Young and Kate Kelland in London; Writing by David Stamp; Editing by Philippa Fletcher and Giles Elgood)