Vietnamese airline Vietjet Air said Monday it will buy 20 widebody Airbus A330-900 planes, doubling its order from the aviation giant in a deal worth an estimated $8 billion.

The budget carrier's chairwoman Nguyen Thi Phuong Thao signed the deal with Airbus as French President Emmanuel Macron looked on as he made an official visit to Hanoi.

The carrier said the order was part of its plans to expand its operations in Asia as well as introducing future long-haul services to Europe.

The announcement comes on top of the 20 A330-900s ordered by VietJet in February last year.

The airline said the A330s would enable it to "increase flights on high-capacity routes across the Asia-Pacific region, as well as to introduce future long haul services to Europe".

The list price of the aircraft was around seven billion euros ($8 billion), an Airbus source told AFP.

"Vietjet remains dedicated to delivering greater connectivity and sustainable air travel for millions of passengers in Vietnam and around the world," Thao said in the Vietjet statement.