Deputy Minister of Transport Nguyen Ngoc Dong said at a meeting on Tuesday that his ministry has asked the Ministry of Foreign Affairs and the French embassy to help facilitate their entry this month.
The embassy said it would respond to the ministry in July since Vietnam and many other countries have suspended all international commercial flights.
The experts from French consultancy firm Apave-Certifier-Tricc returned home during the Lunar New Year break in late January and have been unable to enter Vietnam due to travel restrictions amid the Covid-19 outbreak.
The safety evaluation of the Cat Linh - Ha Dong route awaits their return.
Dong said, "If the French consultants cannot return to Vietnam, the test run of the Cat Linh - Ha Dong railway project cannot be carried out to assess its safety evaluation."
A safety evaluation is needed for commercial operations to begin.
Another major challenge is that most Chinese experts working on the metro line have not been able to enter Vietnam either. Of the 150 needed to complete the remaining work, only 28 have been granted permission so far.
The rest are awaiting completion of formalities and will reach Vietnam by train.
They would be quarantined for 14 days at the Ha Dong Depot, 16 kilometers southwest of downtown Hanoi, Dong said.
Prime Minister Nguyen Xuan Phuc has said the first metro service should begin commercial operations this year.
The Cat Linh-Ha Dong route will run 13 kilometers from the downtown Dong Da District to Yen Nghia in Ha Dong District.
It is one of eight routes planned in the capital city.
Construction began in October 2011 and completion was delayed by years due to various issues.