Two people have been critically wounded after a gunman opened fire on passengers on board a high-speed train travelling to Paris.
A pair of American passengers subdued the gunman, with one of them suffering serious injuries in the process, French interior minister Bernard Cazeneuve said.
He said they had been "particularly courageous and showed great bravery in very difficult circumstances" and that "without their sangfroid we could have been confronted with a terrible drama".
A third person was also hurt in the shooting, said to have involved an automatic weapon, during the journey from Amsterdam to the French capital.
The train was stopped in Arras, 115 miles north of Paris, where a suspect was arrested, interior ministry spokesman Pierre-Henri Brandet said.
Investigators from France's anti-terror police are leading the inquiry, a spokeswoman for the Paris prosecutor's office said.
The man, said to be a 26-year-old Moroccan, was armed with an automatic rifle and a knife, according to France's national railway operator SNCF.
French actor Jean-Hugues Anglade was also reportedly slightly wounded when he broke glass to sound the alarm.
A Foreign and Commonwealth Office spokesman said: "We are aware of reports of shots being fired on a train in France.
"The French authorities have responded. We are in contact with them and are urgently seeking more information."
