Europe's third largest budget airline, Norwegian Air Shuttle, says it plans to adopt new rules requiring two crew members to always be present in the cockpit of a flying aircraft.

Spokeswoman Charlotte Holmbergh-Jacobsson said the new rules will be adopted "as soon as possible" on all commercial flights globally.

She said the decision was taken after details emerged that the co-pilot of Germanwings Flight 9525 that crashed in France on Tuesday had apparently locked himself in the cockpit.

She said the airline's security department had been thinking about the measure "for a while, and today decided on it".

Other airlines, including Finnish national carrier Finnair, stipulate that there must always be two crew members in the cockpit of a flying aircraft.