The absence of controllers on Friday is by far the most widespread since the shutdown began, with one of the worst-hit regions being New York, where 80% of air traffic controllers were out, the agency said.

At least 35 FAA facilities, including several at the largest US airports, reported staffing problems.

Airports affected included facilities in New York, Austin, Newark, Phoenix, Washington, Nashville, Dallas and Denver.

At some airports, delays averaged one hour or more.

The shutdown has forced 13,000 air traffic controllers and 50,000 Transportation Security Administration officers to work without pay.

“After 31 days without pay, air traffic controllers are under immense stress and fatigue,” the FAA said late Friday.

“The shutdown must end so that these controllers receive the pay they’ve earned and travelers can avoid further disruptions and delays,” it added.

The impact on the system would have been far worse on a typical Friday.

However, Halloween evening traffic was 20% lower than usual, which helped mitigate the effects of staffing shortages, airline officials said.

More than 5,600 flights were delayed on Friday and 500 cancelled, according to FlightAware, a flight tracking website.