The fire, which broke out on Wednesday shortly after midnight at OVHcloud, destroyed one of four data centres in Strasbourg, in eastern France, and damaged another, the company said.

There was no immediate explanation provided for the blaze, which erupted just two days after the French cloud computing firm kicked off plans for an initial public offering.

Europe’s largest cloud services provider told clients including the French government, the Centre Pompidou and cryptocurrency exchange Deribit to activate their disaster recovery plans following the blaze.

“Firefighters were immediately on the scene but could not control the fire” in the affected data centre, founder and chairman Octave Klaba said on Twitter. He said the plan for the next couple of weeks would include rebuilding the centres’ equipment and checking their fiber optic connections.

Some 100 firemen fought the blaze which sent a thick plume of black smoke into the night sky. Video images showed firefighters dousing one smouldering, multi-storey building in the early morning as they cooled down the site.

Founded by Klaba in 1999, OVHcloud competes against U.S. giants Amazon Web Services, Microsoft Corp’s Azure and Alphabet Inc’s Google Cloud, which dominate the market.

“OVH is a pretty important hosting company on the internet,” said Mike Prettejohn, who directs UK-based network security company Netcraft. He said the affected servers hosted 3.6 million websites, including niche government platforms in France, Britain, Poland and the Ivory Coast.

Prettejohn estimated that just under 2% of the sites with the French .FR domain extension had been affected.

French politicians have championed OVHcloud as a possible alternative to U.S. cloud services providers, but it has so far lacked the scale and financial clout to dent their market share.

The company said on Monday it had started the process for a potential IPO, without giving details.

The Strasbourg centres were among OVHcloud’s 17 data centres in France, and 32 globally.

Several clients said their websites had gone offline or emails could not be accessed. There was no immediate news of any major data losses.

The Centre Pompidou, one of France’s best known art complexes, said its website was down. Cryptocurrency exchange Deribit said its blog was down but that trading had not been impacted, free chess server Lichess.org said it had lost 24 hours’ worth of games history and news outlet eeNews Europe said its websites were offline.

PR agency Caroline Charles Communication said its data was held at another site but that it had lost access to emails in the middle of Paris Fashion Week.

OVHcloud declined to comment on its fire safety protocols. The site did not pose a toxic risk, it added.