Norwegian’s May passenger carryings grew by 17% to almost 3.5 million over the same month last year.
The rise came as Europe’s third largest low-cost carrier saw capacity soar by 51% year-on-year.
However, the airline said that growth will “gradually decrease” during the autumn and into 2019.
The load factor remained unchanged at 86.5% for the third largest airline operating from Gatwick.
Chief executive Bjørn Kjos said: “We have increased the capacity considerably compared to the same month last year.
“On our long-haul routes, the growth has been strongest outside the Nordics.
“Even with strong capacity growth, the demand is high, demonstrating that our affordable fares, new and more comfortable aircraft and a wide selection of routes attract many new customers.”
He added: “We have been through a long period of strong growth and significant investments, including the establishment of new bases and the training of thousands of new colleagues.
“Our strategy has been to build a strong, competitive company, and going forward we will reap what we have sown for the benefit of our customers, dedicated staff and shareholders.”
The carrier took delivery of a Boeing 787-9 Dreamliner and one Boeing 737 MAX 8 in May.
Norwegian will take delivery of 11 Boeing 787-9s, 12 Boeing 737 MAX 8s and two Boeing 737 800s this year.