Passengers are returning to the Birmingham-Shuttlesworth International Airport after a bomb threat led to a two-hour evacuation and flight delays today.

Birmingham Police responded to a bomb threat at the airport at about 4 p.m., Sgt. Johnny Williams Jr., spokesman for the department, said. He said authorities made the decision to clear the airport and that bomb dogs were brought in to sweep the airport.

Reports have indicated the threat was in the form of a written note.

The Transportation Security Administration said via email just after 6 p.m. that all was clear at the airport. Williams said that nothing was found after the sweep of the airport and that the facility is fully reopened.

The TSA has said they've brought in extra staff to expedite security screening of passengers returning to the airport.

Passengers evacuated from the Birmingham-Shuttlesworth International Airport gather outside the terminal. (Photo by Michael Crump)

Because of the evacuation, a number of flights were delayed or diverted.

Southwest Flight 3424, due from St. Louis at 5:02 p.m., was diverted to Nashville,

, which also said Delta Flight 3947, due in at 4:51 p.m. from Dallas, was diverted to Huntsville.

Hanson Slaughter is a passenger on Delta flight 1304 from Atlanta to Birmingham, which arrived on time this afternoon. But since then, the plane has been on the tarmac, not pulled up to a gate.

"The engines are being shut down on our flight to refuel for a return flight to ATL [Atlanta]," Slaughter texted AL.com. "What a joke! This is outrageous."

According to Slaughter, the pilot of his flight is using a walkie-talkie to communicate with ground staff, and has said that law enforcement will not allow the passengers to deplane.

Bill Keller is also a passenger on that Atlanta flight. The pilot, Keller said, indicated there had been a bomb threat at the airport, but said he couldn't get in touch with anyone at the airport because the control tower had been evacuated.

Tom Arenberg, a passenger on the flight from St. Louis, said the plane landed in Nashville a little after 5 p.m., and passengers were still on the plane at about 5:20 p.m.awaiting word. He said their pilot said there was a vague bomb threat in Birmingham, but "then it got more detailed." Those passengers deplaned at 5:40 p.m. and were told they'd reboard, although they haven't been given a timetable.

Jarvis Jackson was flying home on U.S. Airways from Philadelphia. On a layover in Charlotte, his flight was delayed as social media and news reports trickled in about the situation in Birmingham.

"The airline didn't say what it was ... just that there was a stoppage at Birmingham," Jackson said.

Jackson said overall, the airline handled the situation well but he thought they could have given more details about the scope of the events in Birmingham. He was able to board his flight by about 6:45 p.m. By the time he arrived in Birmingham, the incoming security lines seemed normal, with lots of people waiting to be picked up, he said.

University of Alabama student Kimmy Still was returning home Sunday evening from Austin and had a more chaotic trip.

About 30 minutes into the Dallas-to-Birmingham leg of her journey, the pilot announced there was a bomb threat in Birmingham and the plane would have to land in Little Rock, Ark.

The mood on the plane was calm, she said.

"At first, the pilot told us we could probably take off again at 6 (p.m.), so we all stayed on the plane," Still said.

Then came an announcement that the Birmingham airport could be closed all night and passengers had to leave the plane. Many students on her flight who were concerned that a Monday morning flight would mean missed classes.

Still, who is 17, was told she couldn't stay in the airport overnight and was going to be put back on a plane to Austin.

After haggling with the airline and calling her parents, Still got someone to act as her legal guardian until they got a flight to Birmingham.

"The flight from Little Rock was just like any other flight," Still said. "People did clap when we finally got to Birmingham, though."

"Honestly, it doesn't even seem like anything happened here earlier today," Still said upon arrival at Birmingham about 8:30 p.m.

By 8:30 p.m., flights that had been diverted to Atlanta, Huntsville, Little Rock, Montgomery and Nashville had all arrived in Birmingham. Departing flights were getting back on schedule.

During the evacuation, people who were inside the airport are gathered outside awaiting further word:

Story will be updated with further details.

Here's a tweet from the scene early on: