The gunman is led away (Picture: La Chaine Info)
The gunman, 33-year-old Richard Durn, is reported to be an ecologist and a Green Party activist.
Distraught family members have been arriving at the town hall to identify the bodies.
Premeditated
The gunman's motive remains unclear, but the BBC's Paris correspondent James Coomarasamy says the attack was clearly prepared in advance.
He says the man was known to have psychological problems.
Local Mayor Jacqueline Fraysse, who was leading the meeting, said it was ending quietly when the man opened fire.
"A man got up. He had been sitting in the public area. He shot straight in front of him, and then he moved to where the council members were sitting."
"He said nothing," she said. "It was long. It lasted many minutes."
'He kept firing'
Witnesses said the man calmly reloaded his automatic pistol five times, before pulling out a .357 magnum handgun which he fired at those trying to overpower him.
One official, who asked not to be identified, said someone threw a chair at the attacker and another councillor tried to wrestle him down, "but he kept firing".
"It was a real nightmare, I saw everyone around me crumpling to the ground," he said.
"He was very calm, he didn't look like a crazy person at all."
Police said most of those killed were elected councillors of Nanterre.
Recognised
Crime is the number one issue in France's forthcoming presidential election, and the two main candidates, Prime Minister Lionel Jospin and incumbent President Jacques Chirac rushed to the scene.
Mr Jospin described the killings as a "a terrible tragedy".
"Many officials reacted with great courage to overpower the lunatic," he said.
Mr Chirac, who arrived shortly afterwards, denounced the shootings as an "act of murderous folly".
There is a general feeling in France that crime is on the increase.
Last October, a masked gunman killed four people in the central French city of Tours.