An apparent cyberattack disrupted internet, phones, email and other systems at Seattle-Tacoma International Airport (SEA) for a third day on Monday as Port of Seattle officials worked to investigate the outages and restore full service.

“We’re working around the clock to get necessary systems back online and to mitigate impacts to our passengers,” the airport’s aviation managing director Lance Lyttle said.

Lyttle said the airport is investigating with the help of outside experts and is working closely with federal partners, including the US Transportation Security Administration and Customs and Border Protection. Officials have not released details about the full scope of the outage, but Lyttle said it was not affecting TSA’s ability to screen passengers.

Some airlines, including Delta and Alaska Airlines, reported no service interruptions from the outage. Both of the airlines use Sea-Tac as a hub. Still, the outage did affect the Port of Seattle’s baggage sorting system, prompting airlines to warn passengers to avoid checking bags if possible to avoid potential delays.

The airport also warned travellers to allow extra time at the airport and to use airline mobile applications to get boarding passes and bag tags when possible.

Still, many travellers faced security lines that were longer than normal and long waits at baggage claims and checking. Terminal screens were also out throughout the airport, making it difficult for some to determine their assigned gate.

“Port teams continue to make progress on returning systems to normal operations, but there is not an estimated time for return,” the airport said on Facebook.