The apparently coordinated gun and bomb attacks came as the country, a founder member of the U.S.-led coalition waging air strikes against Islamic State fighters in Syria and Iraq, was on high alert for terrorist attacks ahead of a global climate conference that opens later this month.
Western security sources said they suspected an Islamist militant group was behind the carnage.
At least two explosions were heard near the Stade de France national stadium where a France-Germany friendly soccer match was being played, attended by President Francois Hollande.
The match continued until the end but panic broke out in the crowd as rumors of the attack spread, and spectators were held in the stadium and assembled spontaneously on the pitch.
There were reports of possibly as many as four shootings in central Paris, one of which turned into a hostage taking at a popular rock music venue, witnesses said.
TF1 television said up to 35 people were dead near the soccer stadium, including two suspected suicide bombers in the attack in the neighborhood of Saint Denis, north of central Paris.
Police helicopters circled the stadium as Hollande was rushed back to the interior ministry to deal with the situation. The president's office said he had called an emergency cabinet meeting for midnight (2300 GMT) to manage the crisis.
Police confirmed there had been shootings and explosions at the stadium, but not the number of casualties.
In central Paris, shooting erupted in mid-evening outside a Cambodian restaurant in the capital's 10th district and the Bataclan music hall, where bystanders were evacuated as elite police commandos took up position.
Several witnesses told television stations that up to 60 hostages were being held inside the popular concert venue.
"There are lots of people here. I don’t know what’s happening, a sobbing witness who gave her name only as Anna told BFM TV outside the Bataclan hall. "It’s horrible. There’s a body over there. It’s horrible."
Elsewhere, police cordoned off a wide area around the Petit Cambodge restaurant where witnesses said gunmen armed with Kalashnikov assault rifles had fired at diners through the plate-glass windows, causing multiple casualties.
"I was on my way to my sister's when I heard shots being fired. Then I saw three people dead on the ground, I know they were dead because they were being wrapped up in plastic bags," student Fabien Baron told Reuters.
There were also reports of shootings in rue de Charonne in the 11th district and at the central Les Halles shopping center.
There was no immediate claim of responsibility for the Paris attacks, which came within days of attacks claimed by Islamic State militants on a Shi'ite Muslim district of southern Beirut in Lebanon, and a Russian tourist aircraft which crashed in Egypt's Sinai Peninsula.
Earlier on Friday, the United States and Britain said they had launched an attack in the Syrian town of Rakka on a British Islamic State militant known as "Jihadi John" but it was not certain whether he had been killed.