As many as 20% of U.S. flights could be cut in the coming days if the shutdown continues, Transportation Secretary Sean Duffy said.

The government shutdown is causing canceled flights across the U.S. Here are the routes that are most likely to be canceled, according to a flight attendant.

Major airports appeared to be working largely as normal Friday as airlines canceled hundreds of flights across the United States, but widespread concern that the situation could worsen brought home the effects of

Duffy's comments came two days after he warned there could be far-reaching flight cancellations and disruptions to air travel, pointing to the pressure on the country's air traffic controllers.Start the day smarter.

Follow live updates as flight reductions begin today at 40 high-traffic airports in what officials have described as a "proactive" effort to alleviate pressure points.

Flight delays and cancellations are piling up Saturday across the U.S. after the Federal Aviation Administration cut flights at 40 U.S. airports on Friday.

Hundreds of flights across the United States were canceled starting on Friday, with deeper cuts looming in the coming days.

Critical flight routes between Mexico and the United States face cancellation by November 7. Aeromexico flights from Mexico City airports will be significantly reduced. McAllen International Airport in Texas will also see impacts.