The start of construction for a Japanese-financed subway in the Philippines' urban metropolis of Manila could be pushed back to as far as December next year, a Philippine official said Tuesday.

The Philippine government had said previously that construction of the 355 billion peso (about $7 billion) project would start by the first quarter of 2018, meaning it would be delayed by around nine months.

Jonathan Uy, assistant secretary for investment programming at the Philippines' National Economic and Development Authority, said during a forum in Manila that many factors need to be taken into account, such as the formalization of a loan agreement.