Norwegian Air Shuttle is moving fast to fill the vacuum left by the collapse last week of Sterling Airlines, the Copenhagen-based, Iceland-owned low-cost carrier.

This week it will open a base in Copenhagen and is aiming to have eight to 10 jets operating out of the Danish capital by May, as it scrambles to find more aircraft for its fleet. Some of the parked Sterling jets are a priority initial acquisition target.

Largely unnoticed by many rivals, Norwegian has grown to become the fourth largest low-cost airline in Europe behind the big players Ryanair, EasyJet and Air Berlin. It will fly more than 9m passengers this year with a fleet of 41 aircraft.

The group, which first listed in 2003, is seizing the opportunity offered by Sterling’s bankruptcy to increase the pace of its own expansion despite the threat posed by the economic downturn.

Bjørn Kjos, chief executive of Norwegian, said “it is a huge opportunity”.

He said that the group would replace Sterling as the main low-cost player in the Danish market.

Initially the airline would base two jets at Copenhagen from Thursday flying on six routes to Ålborg, Oslo, Stockholm, Alicante, Malaga and Nice.

It is planning to add further routes from Copenhagen to London, Amsterdam, Rome, Krakow, Prague, Barcelona and Pisa at the pace at which it could bring in more aircraft.

It is also starting new routes on Monday from Stockholm to some destinations previously served by Sterling.

As weaker airlines retrench or collapse, “it’s a good time to expand,” Mr Kjos said. “The market (for aircraft) is much better than last year. . .There are a lot of different airlines that have gone bust. There are aircraft available now.”

Norwegian is also posing an increasing competitive threat to SAS Scandinavian Airlines, the Nordic region’s legacy network carrier, which is struggling.

“They have much higher costs than we have, about twice our level,” said Mr Kjos.

The Oslo-based carrier made clear the scale of its future ambitions by placing an order in August last year with Boeing for 42 186-seat 737-800s for delivery between 2009 and 2014. The deal had a list price value before discounts of $3.1bn.

Deliveries do not start until next summer and the collapse of Sterling has left an urgent need for more capacity.

The group could close deals with lessors for more aircraft this week.

Norwegian got its finances in order just before the financial markets were hit by mayhem this autumn.

This summer it completed a NKr400m ($59.5m) rights issue to finance its deposit for its new fleet orders, and agreed a $160m debt deal with Natixis to fund the pre-delivery payments for the first 10 Boeing jets.