From New York's Liberty Island to Alaska's Denali national park, the US government closed its doors as a bitter budget fight left hundreds of thousands of federal workers idle and halted all but the most critical government services for the first time in nearly two decades.

A midnight deadline to avert a shutdown passed amid congressional bickering, casting doubt on Americans' ability to get government services ranging from federally-backed home loans to supplemental food assistance for children and pregnant women.

For many employees of the federal government, Tuesday's shutdown meant no more pay as they were forced onto unpaid furloughs. For those still working, it meant delays in getting paid.

Park ranger and father-to-be Darquez Smith said he already lived paycheck-to-paycheck while putting himself through college.

"I've got a lot on my plate right now — tuition, my daughter, bills," said Smith, 23, a ranger at Dayton aviation heritage national historical park in Ohio. "I'm just confused and waiting just like everyone else."

The impact of the shutdown was mixed — immediate and far-reaching for some, annoying but minimal for others.

In Colorado, where flooding killed eight people this month, emergency funds to help rebuild homes and businesses continued to flow — but federal worker furloughs were expected to slow it down.

National Guard soldiers rebuilding washed-out roads would apparently be paid on time — along with the rest of the country's active-duty personnel — under a bill passed hours before the shutdown. Existing social security and Medicare benefits, veterans' services and mail delivery were also unaffected.

Other agencies were harder hit — nearly 3,000 Federal Aviation Administration safety inspectors were laid off, along with most of the National Transportation Safety Board's employees, including accident investigators who respond to air crashes, train collisions, pipeline explosions and other accidents.

Almost all of NASA shut down, except for mission control in Houston, and national parks closed along with the Smithsonian museums and the National Zoo. Even the zoo's popular pandacam went dark.

As the shutdown loomed on Monday, visitors to popular parks made their frustration with elected officials clear.

"There is no good thing going to come out of it," said Chris Fahl, a tourist from Roanoke, Indiana, visiting the Abraham Lincoln birthplace national historic park in Hodgenville, Kentucky. "Taxpayers are just going to be more overburdened."

Emily Enfinger, visiting the Statue of Liberty, said politicians need to find a way to work together.

"They should be willing to compromise, both sides, and it discourages me that they don't seem to be able to do that," she said. "They're not doing their job as far as I'm concerned."

Joe Wentz, a retired federal employee from Lebanon, Virginia, visiting San Francisco with his wife, bought tickets to visit Alcatraz on Thursday — if it's open.

Wentz said he's frustrated that some politicians are using the budget to push changes in the Affordable Care Act.

"We've been disgusted a long time that they're not working together," he said.

The shutdown was strangely captivating to Marlena Knight, an Australian visiting Independence national historical park in Philadelphia. She was confounded that the impasse focused on the nation's healthcare system — an indispensable service in her home country.

"We can't imagine not having a national health system," she said. "I just can't believe that this country can shut down over something like a national health system. Totally bizarre, as an Australian, but fascinating."

It turns out an institution as massive as the federal government takes some time to grind to a total halt. Many federal workers were being permitted to come in on Tuesday to change voicemail messages or fill out time cards. But after that, they were under strict orders to do no work, even check their email.

With no telling how long the budget standoff will last, even programs not immediately affected could run out of cash.

Barbara Haxton, executive director of the Ohio Head Start Association, said its preschool learning programs would be in jeopardy if a shutdown lasted more than two weeks. March's automatic budget cuts meant nearly 3,000 children lost access to services and there could be dire consequences if the budget standoff dragged on.

"It's not as though this is a throwaway service. These are the poorest of the poor children," Haxton said. "And our congressman still gets his paycheck. His pay doesn't stop and his health insurance doesn't stop."