Two century-old bridges above a busy Brooklyn subway station have grown so corroded from a lack of maintenance that city officials have begun questioning their structural integrity, engineering records show.

The bridges support the sections of Newkirk and Foster avenues on either side of Newkirk Plaza, which sits above the trench where the B and Q subway lines run. An engineering assessment published by the city last month shows the steel on each crossing is full of holes, and the concrete decks are deteriorating.

Exposed, rusting rebar is in clear view on both bridges. Small, white stalactites are visible on the Newkirk Avenue crossing, a sign that water has seeped through for years.

The city transportation department issued a notice last month calling for a consultant to help devise a plan to fix the crossings. If they were to fall down or become unsafe, it would be a disaster for subway riders in South Brooklyn.

The notice said the bridges were both built in 1907 and “no major rehabilitation took place since then.” Their sorry state highlights a growing challenge for city officials: Much of New York’s infrastructure has outlived its useful life, and repairing it threatens to be highly disruptive for daily commutes.

This steel holds up a street above the B and Q subway tracks in Brooklyn.

"These bridges date back to 1907 and we look forward to rehabilitating them with generational upgrades to last another 120 years," said DOT spokesperson Scott Gastel "We will make sure all proper mitigations are in place for commuters as we proceed.”

The MTA and city transportation department got into a dispute over a decade ago over who was responsible for fixing the bridges, according to  Jerrell Gray, the  chair of Brooklyn Community Board 14.

“The community board was advocating for the agencies to settle those jurisdictional issues since 2012,” said Gray. “That was honestly the main driver why those bridges haven't had improvements since they were built…  Neither agency wanted to take responsibility.”

The city has since taken responsibility for the bridges. But the MTA is in charge of Newkirk Plaza, which is decked over the subway station and is filled with shops, restaurants and a more than 100-year-old barber shop.

Fixing the bridges comes with a host of challenges that could make the work expensive. The notice posted by the transportation department says a repair job may have to work around a sewer line that runs beneath the subway tracks. And city engineers noted they could not find the original drawings for the Foster Avenue bridge.

City engineers have identified dozens of severely corroded spots on the bridges that bookend Newkirk Plaza.

Commuters have come to accept the state of the bridges, but on a recent visit, commuters didn’t seem particularly worried.

“ I don't love the condition of it, you know?” said Sal Swar, a 26-year-old commuter taking in the station's spalling concrete. “It looks kinda s---ty.”

Max Moston, a 55-year-old musician who lives nearby, said he’s used the station for most of his life.

“ This neighborhood remarkably hasn't changed as much as the rest of New York City has changed. It’s always been a little dilapidated, a little livable,” he said. “This bridge, the homeless guys use it as a bathroom, this stop has always been kind of a little rustic.”

Repairs to the bridges are still years away, and it’s not yet clear how the fix would affect subway service on the B and Q lines. The MTA referred all questions on the bridges to the city transportation department.

Gray, the community board chair, said he hoped the transportation department would also take ownership of Newkirk Plaza. If that happened, he said the space would be eligible for more funding and upgrades through city-run programs.

“ Many local businesses aren't happy with what it is now,” said Gray. “They feel like it's impacting their businesses.”