Three US tourists and a 62-year-old man overpowered a gunman allegedly attempting to massacre passengers on a train in France after the crew fled to a safety room.

The drama unfolded on Friday when suspected attacker Ayob El Khazzani, 25, boarded the Amsterdam-Paris express in Brussels.

He was carrying a Kalashnikov assault rifle, a Luger automatic pistol, nine cartridge clips and a box-cutter, investigators say.

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But his attack was stopped when the three Americans and a Briton – two of them off-duty soldiers – charged the gunman and defeated him, eliciting praise from US President Barack Obama. 

While passengers sat vulnerable, crew members ran straight into a safe room and barricaded themselves inside.

The 550 passengers on board the train from Amsterdam to Paris were allegedly about to become victims in a planned massacre.

How they did it: “Let’s get him”

“I looked back and saw a guy enter with a Kalashnikov. My friends and I got down and then I said, ‘Let’s get him’,” Alek Skarlatos, a 22-year-old member of the National Guard in Oregon, told reporters.

Spencer Stone, a US Air Force serviceman, reached the gunman first and was slashed in the neck and hand with a box-cutter.

“At that point I showed up and grabbed the gun from him and basically started beating him in the head until he fell unconscious,” said Mr Skarlatos, who recently returned from service in Afghanistan.

The third American, student Anthony Sadler, said the attacker “didn’t stand a chance”.

“As soon as we saw him, we all ran back there. It all happened really fast,” Mr Sadler said. “He was just telling us to give back his gun. ‘Give me back my gun! Give me back my gun!’

“But we just carried on beating him up and immobilised him and that was it.”

Luckily, the attacker only got off one shot which hit the shoulder of an American passenger who was later taken to hospital.

For some reason, the man’s rifle jammed, and he ultimately aimed empty shots at passengers before being stopped.

The American trio was helped by a 62-year-old British man, Chris Norman. He decided he’d get up to help and add to the “teamwork”.

“I heard a shot. I heard some glass breaking, then I saw someone running down the aisle towards the front of the train,” Mr Norman said.

“My first reaction was to sit down and hide … Spencer overpowered the terrorist in a neck lock and then Alek was in the process of taking his gun. I grabbed his right arm. There was a French man, I think a train driver, who came to take the left.”

Mr Norman removed his necktie to bind the gunman’s hands. 

Incredibly only Mr Stone was taken to hospital, along with another unnamed American passenger, who was hit in the shoulder with a bullet.

Rescuers heroes, train crew defended

US president Obama praised the young men, saying “it is clear that their heroic actions may have prevented a far worse tragedy”.

He called them personally to laud their actions.

French president Francois Hollande will thank the Americans and the Briton in person at the Elysee Palace on Monday.

According to reports terrified passengers slammed on the locked door where the crew retreated to. Witnesses said the terrified crew ran straight into the safe room and locked the door.

Apparently they did not respond to the passengers even once the gunman was stopped.

Rail union spokesman Christophe Sargollo told BFMTV that the staff had acted “for the best security of the train”.

“I insist on congratulating them on their sang-froid,” he said.

Families relieved and proud

Spencer Stone wasn’t at the press conference with his fellow heroes because of the injuries he sustained.

However his mother, Joyce Eskel, said her son called her from a hospital and told her the gunman also tried to shoot him twice but the weapon didn’t work.

“I’m just crying because I could’ve lost my son so easily,” she told the San Francisco Chronicle.

“He’s always been a hero to me. Now he’s an actual hero. He deserves it. He put his life on the line. They all did, and I’m just very, very proud of him. So proud,” she said.

Tony Sadler said his son, Anthony, called him to describe what happened. He said he was first stunned and relieved his son was not hurt or killed.

“I had thought that this trip, you know, going abroad and travelling for a few weeks would broaden his world view, but never did I suspect he would encounter an experience like this,” Sadler told Sacramento television station KCRA.

“He leaves here a young man on an excursion to broaden his world view and to have fun with his buddies, and he comes back France’s national hero.”

– with AAP and ABC