Engineers laid the line's calibration rail, a short trial section used to check and align the route's technical parameters, on Aug. 11, nearly eight months after construction began last December.

Once commercial service starts, the line will cut the trip from Phu Quoc International Airport to the resorts and entertainment complexes on the south of the island and to the APEC Convention and Exhibition Center to about 20 minutes, the developer Sun Group said.

The line uses 1,435 mm standard-gauge track, the international standard, with rails 180 mm high and 25 m long in a specialized 60R2 grooved profile.

Of the 17.59 km route, 14.3 km runs at grade, about 2 km runs underground and four overpasses at intersections account for a further 1.3 km.

The rail package is being supplied and installed by a consortium of state-owned Vietnam Railways and China Railway 16th Bureau Group (CRCC16).

A rendering of the Phu Quoc light rail line on an elevated section. Rendering courtesy of Sun Group

Tran Anh Tuan, deputy general director of Vietnam Railways, said the company had built many projects but the Phu Quoc line was without precedent, citing the island's difficult terrain and adverse weather. It is Vietnam's first light rail line.

Permanent rail laying begins on the at-grade stretch at km 16 and moves to the overpasses and the tunnel in October.

The project carries a total investment of nearly VND9 trillion ($US342 million) under a build-operate-transfer contract. About VND1.8 trillion had been disbursed by early August.

The developer and its contractors are working simultaneously on bridges, the tunnel and the subgrade to stay on schedule for APEC 2027, which Phu Quoc hosts.

Completion is targeted for the second quarter of 2027.

Phu Quoc is Vietnam's largest island at about 570 sq.km, roughly four-fifths the size of Singapore.