Thousands of Warsaw residents have taken their first rides on the Polish capital's second subway line, just over a year later than expected.

The 6-kilometer (4-mile) line that opened Sunday runs under the Vistula river, linking the eastern Praga district with downtown and western districts. It took five years to build and cost some 4.2 billion zlotys ($1.1 billion).

The opening was scheduled for the fall of 2013, but findings of buried, unexploded World War II explosives and a major water leakage that flooded a nearly-finished station delayed the work.

The M2 line is expected to improve public transport for Warsaw's 1.8 residents and has become even more important since the unexpected closing three weeks ago of a major bridge that was damaged by a fire.