Budget carrier Norwegian Air saw higher-than-expected growth in capacity and passenger traffic in May, while income per customer was in line with forecasts.

The Oslo-listed airline, the subject of a recent takeover proposal by Aer Lingus-owner IAG, is rapidly expanding its long-haul business as it seeks to turn around a loss-making business. 

Passenger traffic, as measured by the number of revenue-generating passenger kilometres (RPK), grew by 51% year-on-year in May, while analysts in a Reuters poll on average had predicted an increase of 48.8%. 

The company's yield, or income per passenger carried and kilometres flown, meanwhile stood at 0.36 Norwegian crowns, matching expectations, but down 6% year-on-year. 

"Even with strong capacity growth, the demand is high," Norwegian Air's chief executive Bjoern Kjos said in a statement. 

"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," he added.