French presidential candidate Marine Le Pen has upstaged opponent Emmanuel Macron by making a surprise campaign stop to a home appliance factory.

As Mr Macron was meeting with union leaders from the Whirlpool plant in northern France, Ms Le Pen popped up outside the factory itself, amid its workers in bright-yellow hazard vests, and declared herself the candidate of France’s workers.

The wily campaign move, which French television news channel BFM broadcast live, had the immediate effect of stealing Mr Macron’s thunder.

A worker stands by a mocked coffin reading Whirlpool killed 286 jobs in Amiens (Thibault Camus/AP)

As Ms Le Pen took selfies with people outside the threatened plant, he was shown in a closed-door meeting with union leaders in the town of Amiens, dressed in a suit and tie.

Ms Le Pen, 48, is fighting her second presidential campaign after coming in third in 2012 while Mr Macron, a 39-year-old former investment banker and economy minister, is fighting his first, having never held elected office.

Even before Ms Le Pen’s impromptu appearance, Mr Macron’s intervention in the Whirlpool factory’s future, in a region where Ms Le Pen got the most votes, was fraught with risk.

Emmanuel Macron

The pro-EU centrist had to tread a fine line between defending his programme to tackle France’s chronic unemployment without falling into the trap of making campaign promises that, if he wins, he could struggle to keep.

The factory in Amiens, where the production of dryers is due to stop next year and shift to Poland, joins a list of threatened plants that have become symbolic of job losses in French presidential campaigns.

In the 2012 presidential race, Socialist Francois Hollande travelled to a closure-threatened steel plant in eastern France’s rust belt in a similar pursuit of blue-collar votes.

Union leaders later felt betrayed when the Hayange plant’s blast furnaces were mothballed in a deal that President Hollande’s government struck with steel giant ArcelorMittal.

A man walks past electoral posters of French presidential candidates Emmanuel Macron and Marine Le Pen in Saint Jean de Luz, south-western France

Ms Le Pen has vowed to keep the Amiens plant open if elected, come what may.

Needing millions more votes to beat Mr Macron in France’s May 7 presidential run-off, she has been hammering hard her claims that more French jobs would be lost overseas under Mr Macron’s more economically liberal programme.