Budget carrier Spring Airlines plans to buy 60 Airbus aircraft for $6.3 billion at list prices, it said Thursday, as a Chinese boom in air travel defies slowing economic growth.

China, the world's second-largest economy, is already Asia's biggest aircraft buyer as a growing middle class takes to the skies in ever-increasing numbers.

The Spring Airlines' order includes 45 A320 planes and 15 A321 aircraft from the European maker, all with the fuel-efficient new engine option, according to a statement to the Shanghai stock exchange.

The major plane order comes despite slowing growth in the Chinese economy, which aviation industry officials fear could hurt air travel.

China logged its worst economic performance since the global financial crisis in the third quarter, with gross domestic product rising just 6.9 percent -- its lowest level in six years.

The Shanghai-based airline said the deal, which was signed on Thursday, sets delivery of the planes from 2019 to 2023.

In July, Spring announced plans to buy 21 Airbus A320 planes for 12.45 billion yuan ($1.9 billion), citing growth in both international and domestic air travel, for delivery from 2015 to 2017.

US aircraft maker Boeing, a rival of Airbus, estimates China will add 6,330 new aircraft worth $950 billion to its commercial fleet by 2034.

Spring Airlines began operations in 2005 and flies more than 90 domestic and international routes, according to its website. Its Shanghai-listed stock closed up nearly five percent on Thursday, before the statement was released.

The Chinese government hopes some of the country's future aircraft market will go to its domestically produced C919, a narrow-body jet which will compete directly with the Airbus A320.

A prototype C919 rolled off the assembly line in Shanghai in November, but the first test flight is not expected until 2016 at the earliest, according to officials from its builder, the Commercial Aircraft Corp. of China (COMAC).

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