Fast-growing budget carrier Vietjet Aviation is set to finalise a US$6.5 billion jet order with Europe's Airbus during a visit to Hanoi by French Prime Minister Edouard Philippe on Friday, people familiar with the matter said.

The order for 50 A321neo jets is part of an aggressive investment in the Vietnamese airline's fleet that has provided lucrative business for both Airbus and its U.S. rival Boeing.

It is also a boost for Airbus as it seeks to turn a raft of incomplete orders put together at July's Farnborough Airshow into hard revenues, narrowing a gap against Boeing this year.

The deal is the biggest economic component of an official visit to France's former colony by Philippe from Nov. 2-4, during which he will oversee deals with French firms and hold talks with Vietnamese counterpart Nguyen Xuan Phuc, they said.

Airbus and Vietjet both declined to comment.