The Civil Aviation Authority of Vietnam (CAAV), in a communication to the Ministry of Transport, said this would enable the airport to handle large jet aircraft. Now it can only handle ATR72 turboprop aircraft with a capacity of 72-78 passengers, and 80-seat Fokker 70s.

The CAAV commissioned the Airport Design and Construction Consultancy One Member Limited Liability Company (ADCC) to come up with upgrade plans for the airport on Con Son, the largest only inhabited island in Con Dao, which is in fact an archipelago off Ba Ria-Vung Tau Province.

The company suggested extending the runway from its current 1,830 meters to 2,400 meters, expanding the apron for eight more aircraft, and building a new terminal to increase the airport’s annual capacity from 400,000 now to two million.

The cost of all this is estimated at VND11.7 trillion ($503.4 million), including VND5.3 trillion for extending the runway.

This includes the cost of transporting soil and rocks from the mainland to the island in case it is not possible to source it locally. If it is possible, the cost could reduce by VND2 trillion.

Speaking about land reclamation from the sea to extend the runway, Nguyen Bach Tung, director of ADCC, said it is feasible.

"We have already built a runway on Spratly Islands using this method," he was quoted as saying by the ministry’s Giao Thong (Transport) newspaper.

It would take three to four years in that case, he said.

Do Tat Binh, deputy CEO of the Airports Corporation of Vietnam (ACV), said extending the runway into the sea is not too difficult but "too expensive."

He said the ACV had studied the possibility almost a decade ago but concluded it was "feasible but not economical."

The sea in that area is rough, and there is no guarantee the reclaimed area would withstand it, Binh said.

Instead of extending the runway to allow larger aircraft, more flights should be operated to the island using small aircraft, he added.

Con Dao airport was built by the French in the 20th century, and upgraded in 2003 for commercial use.

Vietnam Air Services Company, a subsidiary of Vietnam Airlines, is the only airline that flies to Con Dao. It has daily flights from Ho Chi Minh City.

Budget carrier Vietjet Air is planning to fly to Con Dao from Hanoi and HCMC using Airbus A319 aircraft with a capacity of 160. Newcomer Bamboo Airways has also expressed interest.

Last year Con Dao received more than 286,000 visitors, up 17.3 percent from 2017, including 32,000 foreign tourists.

There are also speedboats to Con Dao from Ba Ria-Vung Tau and Soc Trang Province in the Mekong Delta.

Con Dao served as a jail for political prisoners during the French colonial era and later that of the U.S.-installed regime in Saigon. They were held in brutal conditions in the infamous "tiger cages." The old prison buildings still stand and are open to the public as a museum tracing Con Dao's history.

The island boasts pristine natural beauty with forested hills, sandy beaches and extensive coral reefs, though it is now threatened by trash overload.