An unidentified customer has ordered four 747-8 Freighters, Boeing confirms on 8 April.

The sale first appeared as an update on Boeing's weekly refresh of its online orders and deliveries database.

It is the first new order logged for the 747-8F since December, when Boeing sold two of the aircraft to its aircraft financing unit. Boeing Capital then reportedly leased the 747-8Fs to Russian cargo firm AirBridgeCargo.

Last year, AirBridgeCargo signed an commitment to buy up to 20 747-8Fs.

Boeing's total backlog for the 747-8 programme now stands at 23 aircraft, including 11 freighters, according to Boeing's online database.

Later this year, Boeing plans to reduce the production rate of 747-8s to 0.5 per month.

Boeing formally launched the original 747-100 50 years ago next week.