Washington DC - Transport Secretary Sean Duffy warned Tuesday that the government shutdown will cause air travel chaos if it lasts another week, worsening staff shortages, snarling airport lines, and closing down sections of airspace.

"So if you bring us to a week from today, Democrats, you will see mass chaos... You will see mass flight delays," he told a news conference in Philadelphia.

"You'll see mass cancellations, and you may see us close certain parts of the airspace, because we just cannot manage it, because we don't have the air traffic controllers."

With the standoff in Congress over vital health care spending set to become the longest in history, Trump's Republicans and the opposition Democrats are facing increasing pressure to end a crisis that has crippled public services.

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More than 60,000 air traffic controllers and Transportation Security Administration officers are working without pay, and the White House has warned that increasing absenteeism could mean chaos at check-in lines.

Airport workers calling in sick rather than working without pay – leading to significant delays – was a major factor in Trump bringing an end to the 2019 shutdown, the joint-longest alongside the current stoppage, at 35 days.

After five weeks of failed votes on a House-passed resolution to reopen the government, the Senate rejected the legislation for a 14th time on Tuesday.

Democrats say the only path to reopening the government is a Trump-led negotiation over their demands to extend subsidies that make health insurance affordable for millions of Americans – the key sticking point in the standoff.

But Trump has insisted he won't negotiate with Democrats until the shutdown is over.