Budget airline Norwegian was hit by stricter travel restrictions in Europe last month.
Passenger numbers fell 90% in September and chief executive Jacob Schram said: “In September several European countries were classified as ‘red’ by the authorities.
“We have seen that as soon as the authorities impose new travel restrictions demand is immediately impacted.
“We are continuously adapting our route network in line with changing demand, but the frequent changes in travel restrictions make forward planning difficult, both for us and our customers.
"Looking ahead, this continues to be a prolonged crisis that is far from over.”
The airline carried 319,370 passengers last month, with capacity down 93%. Its flights were on average just over half full, with a load factor of 52.8%, a fall of 37 percentage points.