French officials were under pressure Thursday to save the jobs of hundreds of French steel workers at factories facing an uncertain future after the collapse of British Steel, whose assets will be sold to pay off its debt load.

"We knew something was wrong but not that the situation was as catastrophic as this -- it's like a gunshot," Djamal Hamdani, a union representative at British Steel's plant in Hayange, northeast France, told AFP.

The site, specialising in steel beams, employs some 420 workers, plus additional part-time hires and subcontractors.

It depends on raw steel supplied by British Steel's factory in Scunthorpe, England, one of the sites that could be sold or shuttered after the company was placed in compulsory liquidation on Wednesday.

"Scunthorpe's closure would lead to the closure of Hayange and of FNSteel in the Netherlands, pure and simple," Hamdani's CFDT union said in a statement.

British Steel bought the Dutch factory at Alblasserdam in 2017, when it employed nearly 300 people.

The firm's failure also jeopardises the futures of some 270 workers at the Ascoval factory in Saint-Saulve, northern France, which British Steel pledged to rescue from imminent bankruptcy just a few weeks ago.

The Ascoval site's future has been up in the air since a restructuring carried out by its former owner in 2015, when Emmanuel Macron, then the economy minister, told workers "there will not be any closure of the site, nor any forced layoffs".

Prime Minister Edouard Philippe said Thursday that "the game isn't over" despite British Steel's collapse, which he attributed to complications from Britain's looming exit from the EU.

"We knew that British Steel urgently needed to build up its capacity in continental Europe because, being based in the UK, it might not have had access to European clients," Philippe told CNews television.

The French government provided a 15 million euro ($16.7 million) loan for Ascoval and British Steel had provided 5 million, while promising an additional 40 million euro shareholder loan.

"I'm being very cautious about this, but I'm fairly optimistic. I think we can do this," Philippe said.

Finance Minister Bruno Le Maire will meet with Ascoval employee representatives Thursday and with Greybull Capital, British Steel's owner, on Friday, a CGT union official, Nacim Bardi, told BFM television on Wednesday.

"For now, the most important thing is to meet our main shareholder Greybull," he said.