OTTAWA -- Government officials say they are in a race against the clock when it comes to building new warships for the navy, with little flexibility for further delays in the multibillion-dollar project.

A long-anticipated competition to pick a foreign design for the ships that will replace the navy's frigates and destroyers opened on Thursday.

The government would like construction on the new warships to start in Halifax around 2020, when the last of the navy's new Arctic patrol vessels is scheduled to be finished.

"Our focus is a continuous build program," said Lisa Campbell, head of defence and marine procurement at the Department of Public Services.

But officials say there is currently a two-year gap between the projects.

Officials want to close that gap to ensure workers and equipment don't sit idle, which will cost taxpayers more money.

That won't be easy, however, as there are many more potential roadblocks that need to be cleared before construction begins.

"From a program perspective, there's not a lot of flexibility," said Patrick Finn, head of military procurement at the Department of National Defence. "Right now, schedule is very important for us. There are some risks emerging that we need to deal with."

The previous Conservative government promised 15 ships at a cost of $26 billion, but the cost was later revised up to $40 billion.

The Liberals have since said they won't discuss how many ships will be built or the budget until more work is done, a position echoed by officials.