Boeing said China's Okay Airways has committed to buy 12 aircraft in a deal worth $1.3 billion.

The deal to sell the 737 series of aircraft, which was reached at the Singapore Airshow, is subject to the approval by the Chinese government, Boeing said.

"We greatly value the ties we have built over the years with Boeing," Okay Airways chairman Wang Shusheng said, according to the Agence France-Presse.

Okay Airways, Beijing-headquartered private airline, said it is in the process of modernising the fleet.

The purchase deal includes eight 737 MAX 8s, three 737 MAX 9s and one next generation 737-900 extended range version.

Several aircraft orders were made on Tuesday, the first day of the Airshow.

US aircraft leasing company Aerolease Aviation said it would buy 10 MRJ90 regional jets from Japan's Mitsubishi Aircraft.

A Singapore-based commercial aircraft lessor also signed a deal to buy five new ATR 72-600 turboprop aircraft from France's ATR.