HANOI (BLOOMBERG) - VietJet Aviation Joint Stock Co, Vietnam's only private airline, signed a US$2.39 billion (S$3.24 billion) order with Airbus Group for 20 more A321 planes, according to a statement from the carrier.

The deal was signed on Tuesday (Sept 6) in the presence of French President Francois Hollande, who is currently visiting the Southeast Asian country. The aircraft will be delivered to VietJet between 2017 and 2020, according to the statement. Late last year at the Dubai Airshow, the low-cost carrier had agreed to buy 30 Airbus A321 planes in a deal worth US$3.6 billion at list prices.

VietJet started operations in December of 2011, and is seeking to expand in a market that's grown at least 20 per cent annually in the last three years, according to the airline.

In May, VietJet said it would buy 100 Boeing 737-Max 200 jets in an order worth US$11.3 billion when US President Barack Obama visited Vietnam.

The airline operates more than 250 flights a day with 50 routes in Vietnam and across the region to countries such as Thailand, Singapore, South Korea, Taiwan, China, Myanmar and Malaysia. VietJet will probably surpass national carrier Vietnam Airlines as the nation's biggest domestic carrier this year, according to CAPA Centre for Aviation.

Vietnam is expected to rank among the world's 10 fastest- growing aviation markets in the next two decades, according to the International Air Transport Association.