Officers on foot and in squad cars fanned across the nervous city, taking up positions outside media offices, along the Champs-Elysees avenue and at entrances to underground train stations.
Investigators have so far been unable to identify the gunman, described by French Interior Minister Manuel Valls as "a real danger".
A source close to the investigation said the police had "received several hundred calls" following an appeal for information from the public.
His motive remains unclear, but police believe the man was also behind an incident on Friday in which staff at a Paris television station were threatened by a gun-wielding intruder.
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The attacker, wearing a cap and wielding a 12-gauge shotgun, opened fire at the offices of left-wing newspaper Liberation at about 10:15 am (0915 GMT) yesterday.
A photographer arriving for his first day of freelance work at the paper suffered buckshot wounds to the chest and stomach.
He was taken to hospital in critical condition. The newspaper later said he underwent surgery and was being kept in intensive care.
Liberation executive Nicolas Demorand said on today the man was "still critical," although he was "in a slightly better state."
"He was in a hopeless state yesterday when he was hospitalised," Demorand told France Inter. "He is however in a critical state and we remain hopeful."
After fleeing the daily's offices in the east of Paris, the same man is believed to have crossed the city to the La Defence business district on its western edge, where he fired several shots outside the main office of the Society Generale bank, hitting no one.