Ingram Publishing/Thinkstock(ATLANTA) — The nation’s busiest airport is in the dark tonight and leaving as many as 100 planes stuck on the tarmac, stranding thousands and causing a ripple effect grounding at least 1,200 flights, after a power outage possibly caused by a fire.

Hartsfield-Jackson Atlanta International Airport, one of the world’s busiest airports, suffered a power outage at around 1 p.m. Sunday. Airport personnel, Atlanta Fire and Rescue officials and Georgia Power staff are on the scene to respond and restore service, a spokesman told ABC News.

With the power still out nine hours later, the airport shutdown forced airlines to cancel flights. Delta, which has a large hub operation in Atlanta, said Sunday evening it had already cancelled approximately 900 Sunday flights and another 300 on Monday. Another 48 flights were being diverted to other airports, the airline said.

Hundreds of passengers on inbound flights were stuck on their planes for hours and hours.

Jenny Bloom, who was on a flight from Florida that landed around 2:30 p.m., was still on the plane four hours later.

“[The pilot] came on about a half an hour ago and actually said that he thinks we’re better off here on the plane than going into the terminal because the power is out and nobody can get out,” she told ABC News around 6:30 p.m. “So I think people on the plane are doing fine. I mean people are not upset, they’re staying pretty calm and it’s been fairly quiet. You know, all things considered I think they’re handling this really well.”

Another traveler described the scary scene in the blackout inside the terminals.

“The lights flickered once. That was really scary,” Muhammad Saeed said. “And then they flickered again and they didn’t come back. And it’s been about an hour now and it’s just pitch darkness in the airport.”

Georgia Power said it believes the outage may have been the result of a fire that caused extensive damage in one of the company’s underground electrical facilities. The fire was safely extinguished by fire crews before Georgia Power could enter the area to assess damage and begin repairs, the company said.

Atlanta Mayor Kasim Reed said there was no evidence that the fire was deliberately set, but a security sweep was being conducted. Because extra personnel had to be brought onto the airport campus to fight the fire, authorities want to make sure the fire wasn’t set to allow someone access to the airport grounds that wouldn’t normally have it, the mayor said.

Ann Mason, who was traveling to South Bend Indiana, told ABC News she saw smoke coming from one of the terminals and that people were told to evacuae.

“We were in Terminal D and we could see fire trucks all along terminal E and black smoke coming from the back probably from Terminal F,” she said. “Terminal D got so bad that they told us to evacuate for the smoke and either got to Terminal C or to leave the building. I decided to leave the building.”

“We were standing here and getting ready to get our boarding passes and the lights just went out all of a sudden,” David Bergeron said. “They went out and then they went back on and then they went back out again, and that was it. We’ve been here ever since.”

Atlanta police said they were trying to get everyone out of the airport, and were asking others not to come.

“We need everyone to refrain from coming to the airport. We literally have no power and the ETA for having power is very vague,” Atlanta Police Sgt. Warren Pickard said.

He said there were no injuries everything has been orderly so far.

Multiple airlines, including Southwest and Delta Airlines, told ABC News they were beginning to deplane passengers by sliding them down airstairs.

Before this move, the FAA confirmed to ABC News there are up to 100 planes stuck on the tarmac.

The FAA’s Air Traffic Control System Command Center stated there were “80 to 100″ planes” parked on taxiways.

The agency said that flights headed to the airport were grounded “due to the power outage,” but also added that the airport’s tower has power and is capable of operating “normally.”

Delays are still expected to continue with the equipment failure at several terminals, the FAA official added.

The airport tweeted earlier that the outage had “impacted several areas in the airport” and that officials were “working to remedy the situation.”

A representative of Delta Airlines, which uses the airport as a central hub, said “diversions are in progress” for flights that were already in the air and headed to Atlanta.

The airline rep told ABC News that there are jets sitting on the tarmac waiting to taxi to various gates.

Thomas Guzik tweeted that he was being rescued from the sky train by firefighters.

And cartoonist Dave Trumbore also took to Twitter, but has been jovial about the situation.

“This started as a joke but the flight attendants *quite honestly and literally* just said they have no snacks left and have rationed us a half-cup of water each!” he wrote.

Hartsfield-Jackson International Airport sends jets to 150 domestic destinations and more than 75 international destinations in 50 countries.

It is one of the busiest airports in the world, with on average 275,000 passengers passing through its terminals every day and with about 2,500 flights arriving and departing.

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