First came the thud and within seconds, there was chaos inside the Metro-North commuter train car: Massive flames entered from all directions. Large pieces of sharp metal flew. Passengers shouted and stumbled over one another, desperate to escape.

George Anastas was returning home to Connecticut from a business meeting in Manhattan when the "nightmare" unfolded -- the rush-hour train he was traveling in struck an SUV on the tracks in Westchester County, killing six people and injuring 15.

"It was terrible," said Anastas, who recounted his hellish experience to Newsday. "They were screaming, falling over each other to get to another car." Chunks of hot metal were "flying all over, hitting people."

Outside the train -- in the frigid darkness of a winter night -- burn victims smothered their wounds with snow.

"I thought I was dreaming it," said Anastas, who escaped the car with his friend after another passenger managed to pry open an emergency exit. Anastas' friend, he said, suffered serious burns to his upper body and is hospitalized.

Others weren't as lucky, he said. Anastas said he witnessed horrific injuries, including one man whose leg was partially severed, apparently by a sharp piece of metal. He saw one person consumed by flames, who he believes died in his seat.

"That will stay with me forever," he said, calling the image "unspeakable."

The first car was completely engulfed with flames by the time Roger King, chief of the Valhalla Fire Department and incident commander, arrived at the scene Tuesday night.

Snow piled high near the train tracks from last week's storm made the rescue mission more difficult.

"It was very chaotic," King said. "The hard part was the train tracks don't get plowed, so even though trains are able to go on them there's still a foot of snow, so everyone was self-evacuating and had to stumble through a foot of snow," he said.

First responders, struggling to navigate the snow, used backboards as sleds to pull people away from the train. Overhead, a Westchester County police helicopter used infrared thermal imaging to search the snowy terrain for possible victims who might have wandered away.

Passengers riding further from the first car of the train felt the thud, too, as it hurtled deeper into the suburbs. In seconds, passengers from the inferno-ridden first car began flooding cars further back. Smoke followed.

Rebecca D'Angelis was in the middle of the train when she felt "a little jolt" that she didn't think was "anything serious."

But she and her fellow passengers, who spoke to Newsday in the hours after the deadly crash, fled the car.

"First came the people, then the smoke," said D'Angelis, of Fishkill. "We kept moving toward the back, packing into the last few cars. And the smoke was....following us."

Some passengers panicked, crying and shouting for help. But most stayed calm, she said.

"There was no one telling us what to do or what was happening," she said. "But we smelled the smoke and saw smoke and... we knew there was a fire at the front of the train."

Finally, "they got the back exit open and we all went out, one at a time. We jumped out the back."

She said when she exited the train and saw the blaze she thought: "I just thanked God I wasn't in that first car. It looked horrible."

She added: "I'm so happy to be alive."

Steve Berg was commuting home from his job as an attorney in the city in the third or fourth car from the front of the train, when the accident occurred. He stayed calm, he said, focusing on moving toward the rear of the train to escape, while other passengers jumped from emergency exits.

"I'm trying to stay calm, but it's going through my head that 'this fire could spread, and I've got to find a way to get out of here.' " said Berg, 47, of Chappaqua.

He said some passengers were jumping out emergency exits. He continued moving toward rear of train and eventually, with many other passengers, jumped out a steep exit with the help of two passengers on the ground who were helping people down one by one.

"It was scary. I'm thinking, I've got a fire here, and I'm trapped on a train. The main thing going through my mind is the question, 'could the train blow up?' "

The view from outside the doomed locomotive was equally horrible. Derrick Gilliam, of Hawthorne, said he was driving toward Commerce Street when he witnessed the collision between the Mercedes and the train.

"It basically created a fireball," said Gilliam. "It was just this fireball moving along the tracks, pushing the vehicle. The whole first car of the train was just a big ball of fire."

Gilliam said he hadn't seen how the Mercedes got onto the tracks, only the collision, but said the railroad crossing bars were down when the fire erupted.

"It was a direct hit," he said, "Just a tremendous, tremendous impact."

Back in the first car, Chris Gross saw several people seriously injured as the train filled with fire. He helped several people to safety, he said.

The healing process for those traumatized by what they saw on the doomed train would be long and arduous, he said.

"I'm just trying to decompress," said Gross. "We survived something horrific."

With Candice Ruud