Parts of Terminal 4 at Phoenix Sky Harbor International Airport were closed on Sunday morning, resulting in flight loss and cancellation of many flights.

Gregory Roybal, spokesman for the airport, said the east side of the terminal, before the security checks, had been evacuated. Three of the four security checkpoints were closed and the PHX Sky Train did not drop passengers at Terminal 4.

"The police are trying to solve this problem as quickly as possible," Roybal said in an email.

Roybal said travelers should avoid getting to Terminal 4 until the situation is resolved. Air Canada, American Airways, British Airways, Southwest Airlines, Volaris, WestJet and Condor were affected by the partial closure.

The airport said in a tweet that the airlines were aware that passengers were struggling to get to their doors.

At least 30 Southwest flights canceled before 10:30

Dian Squire spent hours in the hall of the Sky Train while his American Airlines flight to Detroit was delayed several times. He said dozens of people were sitting on the floor waiting for information from the Transportation Security Administration or airport staff.

"It seems a little poor from the point of view of crowd control," he said.

Airport volunteers brought therapy dogs to help calm the growing crowd. Passengers speculated about the possibility of planes taking off or landing. Squire said the stranded travelers did not seem too frustrated with the situation.

"The people are surprisingly calm," Squire said. "I think a security threat is more manageable in people's minds than a delay on the plane for other reasons, and I bet it's different for people stuck in the terminal itself. "

Police in Phoenix did not immediately respond to Arizona Republic's inquiries on Sunday.

It was not clear when the terminal would reopen.

The Arizona Transportation Department said that the exit of National Highway 143 to Sky Harbor Boulevard was also closed for investigation.

This is a story in development. Check for updates.

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