The city People's Committee said at a meeting with the People's Council on Monday that the elevated section of the route could be completed this year and the entire line in 2027.
It cited several reasons for the delay, including difficulties in acquiring land, "low capabilities" of contractors and consultants and lack of coordination between various construction units, the inconsistencies between international contracts and Vietnamese laws, and the impact of Covid-19.
It said a cost increase is inevitable due to exchange rate fluctuations and extra construction tasks.
The government is set to fund the project, whose cost will increase from VND32.9 trillion to VND34.8 trillion ($1.48 billion).
The capital's second metro line will run 12.5 kilometers from Nhon in the western district of Nam Tu Liem via Kim Ma Street to the downtown Hanoi Railway Station.
Work on it began in 2010 at an estimated cost of $1.2 billion, but several delays pushed it up to almost $1.5 billion.
The city's first metro route, Cat Linh - Ha Dong, also the country's first, was completed last November.