Describing President Donald Trump's decision to close U.S. borders to EU citizens as an "aberration", Finance Minister Bruno Le Maire said the move had triggered a historic sell-off on Thursday that saw shares in many of France's top companies collapse.

"We will help all companies in which the state has a stake, Air France, Renault," Le Maire said on French television channel BFM TV.

"What ever it costs we will be at their side and will support them," he added without detailing how the government could help such companies.

While Air France KLM and Renault have been hit hard in the sell-off, so has airport operator ADP, which the government had hoped to reduce its stake in. Le Maire said the market conditions were far from opportune for that.

Other big companies in which the state holds a stake such as energy group EDF, utility Engie and defence group Thales have been less impacted.

So far the French government has focused on helping small and mid-sized companies with a series of measures ranging from state-financed short work time scheme for workers whose hours are cut to loan guarantees for small firms struggling with cashflow problems.

"At the end of the day, it will cost dozens of billions of euros, that how much we can expect," Le Maire said, giving the clearest picture yet how much the crisis would cost the government finances.

Le Maire's German counterpart Olaf Scholz has suggested increasing public investment in infrastructure by 12 billion euros until 2024. He has also proposed pulling forward the already agreed abolition of an income tax surcharge by six months at a cost of some 5 billion euros.

Italian Prime Minister Giuseppe Conte, whose country is the worst-hit in Europe, pledged this week to ramp up spending by allocating 25 billion euros to support firms and families.

(Reporting by Leigh Thomas and Sudip Kar-Gupta; editing by Jason Neely and David Evans)