The train, heading from Paris to Limoges, derailed here, about 20 miles south of Paris, and split into two. Witnesses said that the intercity train — not one of France's TGV express services — appeared to be going unusually fast and veered off the track as it entered the station, where it was not scheduled to stop. Cars smashed into one another and some overturned.
"The death toll is evolving constantly at this point, and unfortunately it will probably rise," said Manuel Valls, the interior minister. "At this stage, there are seven people dead, several dozen wounded, and some of them are serious."
Michel Fuzeau, the local police chief, said a dozen people were seriously wounded, nine of them very seriously.
Guillaume Pepy, the president of the French national railway company, SNCF, said at least 370 people were on the train, many of them heading home for a holiday weekend or to central France for summer vacations. The annual national holiday of Bastille Day is on Sunday.
The train's third and fourth cars derailed first, then knocked four other cars off the track, Mr. Pepy told reporters, his voice breaking. "Some cars simply derailed, others are leaning, others fell over," he said. But he said there was no immediately obvious cause for the derailment.
The accident took place at 5:14 p.m., the SNCF said, not long after the train, Intercités No. 3657, left the Paris station of Gare d'Austerlitz. Some people were still trapped in the train more than two hours later, Mr. Pepy said.
Pictures on television showed one of the carriages smashed against a platform at Brétigny-sur-Orge station as rescue workers helped passengers to safety.
"Everyone is running in every direction. There is panic," the town's mayor, Bernard Decaux, told the newspaper Le Parisien. "It is an apocalyptic scene. We are trying to organize things."
He said that three cars had smashed into one another, while another was lying on its side nearby, its top split open. Photos of the scene showed that one car had mounted the passenger platform, dislodging part of the roof.
Dozens of emergency and police vehicles rushed to the scene, and hospitals in the southern Paris region were put on alert.
President François Hollande headed to the scene when the seriousness of the accident became clear.
"Most of the people who suffered minor injuries have been taken care of," said a local lawmaker, Michel Pouzol. "We are going to have to empty the carriages completely to see if there are victims or not."
The train was traveling on part of the track used by the busy suburban railway, the RER C.
Maïa de la Baume reported from Brétigny-sur-Orge, and Steven Erlanger from Paris.
