Hong Kong flag carrier Cathay Pacific ordered four additional long-haul planes from Boeing on Friday, a week after it ordered 21 Boeing 777-9X planes, in a move to modernise its fleet.

The airline said it would purchase an additional three Boeing 777-300ER passenger planes along with a Boeing 747-8 freighter, with a total list price of HK$7.4 billion ($954.25 million).

Cathay did not reveal the amount it is paying to the US manufacturer, but airlines usually negotiate a discount from a plane's catalogue price.

"Both the 777-300ER and the 747-8F offer a highly efficient solution on Cathay Pacific's ultra-long-haul routes," the airline's chief executive John Slosar said in a statement released Friday.

Slosar said the 777-300ER's, which are expected to be delivered in 2015 and the 747-8F, to be delivered in 2016, combine "superb operating economics with a significant reduction in emissions".

Cathay last Friday ordered 21 long-haul Boeing 777-9X planes, the aircraft manufacturer's newest member of the 777 family, at a list price of $7.48 billion.

The yet-to-be launched 777X series includes advanced technology including composite wings and engines that Boeing says consume 20 percent less fuel than today's model.

The airline said the planes, which will seat up to 400 passengers and be delivered between 2021 and 2024, were ideal for long-haul destinations in North America and Europe.

The airline said in August it swung to a lower-than-expected net profit of $3.1 million in the first six months, after losing money in the same period of 2012. Gains in passenger numbers were offset by persistently high fuel prices and falling cargo revenue.

This year, Cathay has increased daily services to popular destinations such as Los Angeles, Chicago and London.

The airline is set to take delivery of 93 aircraft between 2014 and 2024 at a total list price of $28.63 billion.