Total has flown in 10-20 specialist engineers to tackle the leak and enlisted the services of Wild Well Control, which was heavily involved in the BP's Deepwater Horizon oil spill in the Gulf of Mexico in 2010.
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Nearly 1,000 properties have been left without power, and road users have been warned of potentially hazardous conditions.
It follows a surprise summit between South Korea's Moon Jae-in and the North's Kim Jong-un.
Organisers issued a warning about a “dangerous high strength or bad batch substance on site”.