Travelers across the United States prepared on Thursday for potential chaos ahead of widespread flight cancellations ordered by authorities due to the federal government shutdown.

On Friday, airlines will begin implementing a 10-percent reduction in flights in 40 high-traffic areas of the country, complying with a Federal Aviation Administration order made on safety grounds.

More than 650 U.S. flights scheduled for Friday were preemptively canceled on Thursday, according to tracking website FlightAware, with the number increasing over the course of the day.

American Airlines said in a statement it was reducing its flight schedules "amounting to 220 flights cancelled each day."

Delta Airlines was axing about 170 flights scheduled for Friday, the carrier said, while broadcaster CNN reported Southwest Airlines nixed 100 flights set for that day.

The shutdown has left tens of thousands of air traffic controllers, airport security staff and others without pay, causing personnel shortages.

On Thursday, more than 5,500 U.S. flights were delayed, with 160 cancellations, FlightAware data showed, with travelers facing long lines at security checkpoints.

Major airports were impacted, with travelers at Boston and Newark airports facing average delays of more than two hours, and those at Chicago's O'Hare and Washington's Reagan National more than an hour.

Authorities said they wanted to act before an accident occurred.

"We're not going to wait for a safety problem to truly manifest itself, when the early indicators are telling us we can take action today to prevent things from deteriorating," said FAA Administrator Bryan Bedford.

Peak travel season

The measures come as the country enters its busiest travel time of the year, with the Thanksgiving holiday just weeks away.

The new cancellations could affect thousands of flights every day. Flight reductions will begin at four percent on Friday and rise to 10 percent, media outlets reported.

Flight reductions are set to hit some of the country's busiest airports, including Atlanta, Newark, Denver, Chicago, Houston and Los Angeles.

Implementing the order on short notice will be a challenge for airlines, which operate complex networks that rely on many moving parts and personnel.

United Airlines and Delta, two of the country's largest carriers, have said they are complying with the order but that it would not affect their international routes.

United added that "hub-to-hub" flying would also not be affected, indicating cancellations might hit more local routes.

Senators fail to find path out

Federal agencies across the United States have been grinding to a halt since Congress failed to approve funding past September 30, with some 1.4 million federal workers, from air traffic controllers to national park rangers, still on enforced leave or working without pay.

On Thursday, the Senate failed again to agree on a deal to end the record-long shutdown. Republicans said they offered Democrats a path to reopening the government that included a short-term stopgap funding measure and a package of full-year appropriations bills to pay for agriculture programs, including food assistance, military construction, veterans affairs and the legislative branch.

In bipartisan talks, Republicans have also shown an openness to reversing some of the mass federal workforce layoffs ordered by President Donald Trump's White House and protecting federal jobs from future cuts.

Democrats demand that Republicans agree to negotiate an extension of federal healthcare subsidies before reopening the government. Republicans say the government must reopen first.

The Senate is expected to vote again on Friday. It would need at least eight Democrats to break with their party to reopen the government. Up until now, only two Democrats and an independent who caucuses with them have been willing to do so. 

(With input from agencies)