Beijing (AFP) - Boeing and China's first privately owned airline, Okay Airways, have finalised a $1.4-billion order for five Dreamliner jets, the two companies said on Thursday.

The purchase of the five 787-9 long-haul aircraft by the Beijing-based airline was signed off in the United States on Wednesday and announced on Thursday via the companies' official accounts on Chinese microblogging site, Weibo.

Okay Airways currently has a fleet of 26 single-corridor Boeing 737 planes, which fly to 70 destinations in China and elsewhere in Asia.

The Chinese company had signed a preliminary agreement to buy the planes back in June, when it has also made a firm order for 15 medium-sized 737 MAX planes at a catalogue price of $1.8 billion.

"We are committed to investing in our aircraft fleet in order to keep growing ahead of the market and enhancing our customers' flying experience," said Okay Airways president Li Zongling, according to China's official news agency Xinhua.

He added that the order would strengthen the airline's plans to expand into the long-haul market.

Chinese companies are on the whole profiting from the country's spectacular rate of aviation expansion, fuelled by a growing middle class and a rapidly developing tourism industry.

But competition on international routes is becoming more intense, with China's three airlines -- Air China, China Southern and China Eastern -- fighting it out to lead the sector.