A busy California airport was forced to run without air traffic controllers for over five hours amid the ongoing government shutdown.

From around 4:15 p.m. to 10 p.m. local time on Monday, Oct. 6, Hollywood Burbank Airport in Los Angeles had no air traffic controllers in the Burbank tower, local news outlets ABC7 Los Angeles, KCAL News and Fox 11 Los Angeles reported. Southern California TRACON (Terminal Radar Approach Control), an approach and departure team out of San Diego, was instead relied upon to handle traffic remotely.

Over 80 flights were hit with delays and several others were canceled amid safety concerns, according to Fox 11 Los Angeles.

The shortage in air traffic controllers came on day six of the government shutdown. The 13,000 air traffic controllers and around 50,000 Transportation Security Administration (TSA) employees are expected to continue working without pay, which has led to many employees nationwide calling in sick.

“We are tracking sick calls, sick leave,” said U.S. Secretary of Transportation Sean Duffy in a press conference early on Monday, per ABC7 Los Angeles. “Have we had a slight tick up in sick calls? Yes.”

“And then you’ll see delays that come from that, right? Because again, our priority, again, I want to see your flight not be delayed,” Duffy continued. “I don’t want you canceled, but our priorities are safety.”

“So if we have additional sick calls, we will reduce the flow consistent with a rate that’s safe for the American people,” he concluded.

Duffy also said, per KCAL News, “If we think theres issues in the air space we will shut it down, we will close it down, delay.”

Delays at Hollywood Burbank Airport ranged in time, with the longest reported being almost four hours as of 5 p.m. local time on Monday, per the Los Angeles Times. The average was two hours and 31 minutes due to runway construction coinciding with the staffing shortage.

The National Air Traffic Controllers Association (NATCA), the union representing air traffic controllers, said the situation at Hollywood Burbank Airport was “an example of how fragile our aviation system is” in a statement obtained by the Los Angeles Times.

“NATCA has consistently warned that the controller staffing shortage leaves the system vulnerable, and today’s events underscore the urgent need to accelerate training and hiring,” the union said, per the outlet.

As the government shutdown continues, NATCA reminded workers on Monday that “participating in a job action could result in removal from federal service” and that it is illegal, per Reuters.

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NATCA is working alongside the FAA to mitigate travel disruption while fighting to increase hiring rates of air traffic controllers, the Los Angeles Times reported. According to the union, many employees currently work 10-hour shifts up to six days a week.

Staff shortages caused delays at several other airports on Monday, including Newark Liberty International Airport in New Jersey and Denver International Airport, NBC News reported, citing the FAA.

Hollywood Burbank Airport reassured travelers that flights were going ahead despite the issues in a statement shared on Monday.

“Operations are continuing at Hollywood Burbank Airport,” the statement read on the airport’s Facebook page. “Please check with your airline – before arriving at the airport – for updates on possible delays or cancellations.”

Jeffrey Price, professor of aviation at the Metropolitan State University of Denver, said travelers will notice longer lines at security and increased flight interruptions as the shutdown continues.

“The system does become a little bit more brittle, and the longer this goes, the more the traveler is going to notice it,” Price told ABC7 Los Angeles.

The FAA, Hollywood Burbank Airport, the National Air Traffic Controllers Assn. and the U.S. Department of Transportation did not immediately respond to PEOPLE’s request for comment on Tuesday, Oct.7.