PARIS — Masked gunmen with automatic weapons opened fire in the offices of a French satirical newspaper on Wednesday in Paris, the police said, killing 12 people and then escaping in a car.

je suis Charlie pour le droit à la satire , contre les lâches et en solidarité avec #CharlieHebdo pic.twitter.com/TtzL52ZeDD

— NicoladiaZ (@nicoladiaz) January 7, 2015

President François Hollande said the attack on the weekly, Charlie Hebdo, was “without a doubt” an act of terrorism and raised the nationwide terror alert to its highest status. He said that several terrorist attacks had been thwarted in recent weeks.

The gunmen were still at large hours after the shooting. The French authorities added additional security at houses of worship, news media offices and transportation centers. Some schools were on lockdown and an extensive manhunt for the gunmen was being carried out across Paris.

A senior French prosecutor said the victims included two police officers, including one assigned to guard the newspaper’s offices and its top editor. The second officer was shot and killed as he lay on the ground, the police.