SEATTLE (AP) — An apparent cyberattack disrupted internet, phone, email and other systems at Seattle-Tacoma International Airport for the third straight day Monday as Port of Seattle officials worked to investigate the outages and restore full operations.

“We are working around the clock to bring the necessary systems back online and mitigate the impact on our passengers,” the airport’s aviation executive director, Lance Lyttle, said at a press conference on Sunday.

Lyttle said the airport is investigating the incident with the help of outside experts and is working closely with federal partners, including the Transportation Security Administration and Customs and Border Protection. Authorities have not released details on the full extent of the outage, but Lyttle said the TSA’s ability to screen passengers was not affected.

Some airlines, including Delta and Alaska Airlines, reported no service disruptions caused by the outage. Both airlines use Sea-Tac as a hub. However, the outage affected the Port of Seattle’s baggage sorting system, prompting airlines to warn passengers not to check bags if possible to avoid potential delays.

The airport also advised travelers to allow extra time at the airport and, if possible, to use airline mobile apps to obtain boarding passes and baggage tags.

Still, many travelers had to wait longer than usual at security and endured long waits at baggage claim and check-in. In addition, terminal screens were down throughout the airport, making it difficult for some to find their assigned gate.

“Port teams continue to make progress in restoring systems to normal operation, but there is no estimated time for restoration,” the airport wrote on Facebook on Sunday.