Scottish oil refinery Grangemouth has started to shut down ahead of a two-day strike that threatens to create major fuel shortages in Scotland and the north of England for up to a month, management said.

Workers are due to launch the two-day strike on April 27, forcing the Ineos refinery to close with a significant impact on the North Sea Forties pipeline system that terminates there.

Ineos said it started to shut down the 200,000 barrels per day former BP refinery late on Friday to make it safe ahead of the planned industrial action.

"The union is well aware that a 48-hour strike will cause fuel chaos in Scotland and the North of England for weeks on end," Ineos Olefins chief executive officer Tom Crotty said in a statement.

"This is a huge oil refinery and they know you can't just turn it on and off like a tap. A month is our best guess but safety considerations will be at the forefront of everything we do."

Workers are striking over changes to the final salary pension scheme.

Grangemouth's general works manager Gordon Grant said it would not be possible to meet all the fuel needs of Scotland and the north of England while the refinery was shut.

"200,000 barrels a day is a lot of fuel," Grant told Reuters. "It's generally accepted that it's not feasible to supply Scottish fuel needs by tanker."

According to union Unite the strike over changes to refinery workers' pension scheme would be Britain's first oil refinery strike in 73 years.

The union says Ineos made unnecessary reductions to the value of its members' pensions without their agreement, while Ineos says the pension scheme remained a generous final salary scheme and would be fully funded.

Strike news boosted oil markets on Friday as port workers at France's Fos-Lavera refining hub blocked 23 ships and extended their strike until Saturday. Oil prices hit a record high of $117 per barrel in New York.