A few cracking sounds and some dust preceded the horrific crash as a 98-foot portion of the concrete, steel and glass roof caved in just before 7 a.m.
Rescue workers compared the pile of twisted steel, boulders of concrete and shattered glass to an earthquake scene. They sent in sniffer dogs in search of victims.
At least five people were killed in the collapse and three others injured. The victims were likely passengers, said Hubert de Mesnil, director general of Paris airports. Officials said there could be a sixth death. Victims' identities were not immediately known.
An Air France flight had arrived from New York just ahead of the collapse and another from Johannesburg, South Africa. A third plane was taking off for Prague. Michel Sappin, prefect for the Seine-Saint-Denis region, where Roissy is located north of Paris, said there was only a moderate number of passengers in the terminal at the early hour.
"It looks pretty bad out there," said Amy Haight, 30, arriving later from Houston with her husband, Nelson, for a friend's wedding. She said she saw the collapsed building and dozens of rescue vehicles as her plane landed. "It's so sad, it's so scary. My God, we're so lucky."
The roof fell onto a waiting area in the futuristic, cylindrical terminal that sits on pylons, pulling down the outer walls and crashing through a boarding ramp and onto several parked cars below.
President Jacques Chirac asked that investigators quickly determine the cause of the collapse on a cool but sunny day. Two separate probes were being opened.
Transport Minister Gilles de Robien said there was nothing to indicate a terrorist attack.
The terminal, a tunnel-shaped construction that is hundreds of meters long, was evacuated and immediately shut down, delaying scores of flights. Concerns over the image of Paris' largest airport were immediately apparent.
"The consequences are obviously grave for us since we have to manage the movement of planes with one less terminal, grave in terms of image since this was our showcase jewel," said Pierre Graff, president of Aeroports de Paris, which runs Paris' airports.
The tragedy comes as France braces for the influx of summer tourists who will pour into Charles de Gaulle airport.
The $900 million terminal, with slots for 17 aircraft, opened to the public last June 25 after at least two construction delays. The French television station LCI said the delays were caused by safety issues.
A huge light fixture fell in the departure area as inspectors were checking the facility, said Rene Brun, director of Charles de Gaulle airport, confirming press reports.
He said there also were leaks in the ceiling. However, Brun and other officials said the problems were not structural.
"There were never signs of cracks or other major abnormalities," Brun said.
The terminal was designed for a capacity of 10 million passengers per year. Its distinctive vaulted ceiling is honeycombed with hundreds of square windows that bathe the area inside with sunlight.
Some warning signs appeared just ahead of Sunday's roof collapse, said Graff, the president of Paris airports.
"Some witnesses heard something cracking just before the collapse. There were cracks and some dust from the concrete," he said.
Brun said police called to the scene asked people to evacuate. However, the roof caved in within two to three minutes.
"It's the structure that gave way, the structure itself," said Mesnil, the director-general of the Paris airports.
Hundreds of rescue workers rushed to the scene and temporary hospitals were set up on the tarmac and inside the terminal as sniffer dogs searched the twisted rubble for signs of bodies.
"We're working in extremely difficult conditions," said Interior Minister Dominique de Villepin, adding that earthquake-style rescue operations were used in the delicate task of combing through rubble.