Norwegian Air will cancel more than 4,000 flights and temporarily lay off up to 50% of staff in response to President Donald Trump’s European travel ban and the coronavirus pandemic.

As the airline crisis deepened on Friday, British Airways boss Alex Cruz has written to the airline’s 45,000 workers in a note titled “survival of British Airways”, according to reported.

Cruz said the coronavirus pandemic was worse than the global financial crisis, the SARS outbreak and 9/11. “It is a crisis of global proportions like no other we have known,” he said, warning that jobs would be lost at least in the short term.

Norwegian Air said it had decided to ground 40% of its long-haul fleet and cancel 25% of short-haul flights until the end of May.

Norwegian Air Shuttle stock plunged 22% late on Thursday before climbing 15% on Friday as part of a wider market recovery — the share price remains 77% down year-to-date.

The majority of Norwegian Air flights to the U.S. from Amsterdam, Madrid, Oslo, Stockholm, Barcelona, and Paris will be canceled, it said, but routes between London Gatwick and the U.S. will operate as normal.

As the U.S. ban on travel from Europe doesn’t include the U.K., Norwegian Air said it planned to reroute “as many customers as possible” through London.

Donald Trump announced a 30-day ban on travel from Europe’s Schengen Area to the U.S. earlier this week, which will come into effect on Saturday.

The Schengen Area consists of 26 countries, including France, Germany, Spain, and Italy. U.S. citizens are exempt from the ban but will face medical screening on their return to America.

Read: Trump Bans European Air Travel. Here’s What It Means for Airlines.

Norwegian Air Chief Executive Jacob Schram said: “The new restrictions imposed further pressure on an already difficult situation. We urge international governments to act now to ensure that the aviation industry can protect jobs and continue to be a vital part of the global economic recovery.”

The company added that due to the “extraordinary market situation” and drop in customers and production it was forced to cut costs. “This unfortunately also includes temporary layoffs of up to 50% of our employees and the number may increase,” it said on Friday.

Airline stocks rallied on Friday, with German carrier Lufthansa up 19% and Air France-KLM up 25%.

Looking ahead. Airlines are having a turbulent year to say the least, and Trump’s shock European travel ban has sent stocks nosediving even further. Norwegian Air’s measures may sound drastic, particularly laying off half of its staff, but it just highlights the scale of the problems facing the sector as the coronavirus crisis deepens. The global pandemic shows no signs of slowing and travel will be disrupted for some time yet.