The loss, reported by the $556 million expressway’s project monitoring unit, can cause trash to clog the drains when it rains and lead to flooding, officials said.
All the grates stolen were in Quang Yen Town in the northern province of Quang Ninh. They are estimated to cost VND100 million ($4,400) in total.
The drain gates were large enough for a single car tire, and could therefore cause traffic accidents, the Quang Ninh Transport Department has said.
“The unit is currently working to get new grates and the police are already investigating the robbery,” said Vu Van Khanh, head of the province’s Department of Transport.
Built at a cost of VND13 trillion ($556 million), the 24.6-kilometer Ha Long-Hai Phong Expressway connects National Highway 18 in Ha Long's Dai Yen Ward with the Hanoi-Hai Phong Expressway in Hai Phong's Hai An District.
Work on it began in September 2015 and was scheduled for completion last March, but this was delayed twice. It is now scheduled to be open to traffic early next month.
The expressway is among a series of infrastructure projects aimed at boosting the tourism industry in Quang Ninh, home to the world famous bay Ha Long.
Others include an international airport in the province’s Van Don District and a new expressway between Ha Long and the proposed special economic zone in Van Don, both of which are scheduled for completion later this year.
Quang Ninh welcomed 6.6 million visitors this year as of May, including 2.17 million foreigners, according to official figures. Tourism revenues for the period rose 32 percent year-on-year to VND11 trillion ($472 million).