WASHINGTON, United States (AFP) — Travellers across the United States (US) 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 per cent reduction in flights in 40 high-traffic areas of the country, complying with a Federal Aviation Authority (FAA) order made on safety grounds.

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

More than 10,000 flights to or from the United States were delayed last weekend, according to the tracking service FlightAware, with travellers already facing long lines at security checkpoints.

On Thursday, 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.

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

The cancellations could affect thousands of flights every day. Flight reductions will begin at four per cent on Friday and rise to 10 per cent, 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 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.

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 park wardens, still on enforced leave or working without pay.

Many in high-stress aviation-related jobs are now calling in sick and potentially working second jobs in order to pay their bills, US Transportation Secretary Sean Duffy said on Wednesday.

FAA Administrator Bedford said the situation was unprecedented.

“I am not aware in my 35-year history in the aviation market where we’ve had a situation where we’re taking these kinds of measures,” he said Wednesday.

“Then again, we’re in new territory in terms of government shutdowns.”