The gunmen "will be chased as long as necessary, so that they can be stopped and be brought before judges," French President Francois Hollande said.

Earlier, the President said, "This is a terrorist attack, there is no doubt about this."

[Latest update at 8:19 a.m. ET]

• U.S. President Barack Obama has been briefed with limited details about the Paris attack, White House spokesman Josh Earnest told CNN on Wednesday morning. Earnest said he is not aware of any imminent threat to the United States.

• Four people wounded in the attack are in critical condition, Hollande said.

• The French President is calling an emergency Cabinet ministers' meeting, set for 8 a.m. ET Wednesday (2 p.m. local time), at the Elysee Palace.

• Journalists and policemen are among the victims in the attack, said Hollande, who added that at least four were seriously wounded. He said it would be a few hours before a definite number of injured is known.

• British Prime Minister David Cameron reacted to the deadly shooting, saying on Twitter: "The murders in Paris are sickening. We stand with the French people in the fight against terror and defending the freedom of the press."

Two heavily armed men entered the Charlie Hebdo office in Paris' 11th district and opened fire, SPG police union spokesman Luc Poignant told CNN affiliate BFMTV.

He said the attack, close to Place de la Bastille, at least three police officers were injured. The Paris mayor's office said at least six people were wounded, according to BFMTV.

The French government raised the country's security alert system to its highest level Wednesday after the attack, according to French media.

Hollande and other senior government officials were due to arrive at the scene of the shooting, BFMTV said.

A witness who works in the office opposite the magazine's told BFMTV that he saw two hooded men, dressed in black, enter the building with Kalashnikov submachine guns.

"We then heard them open fire inside, with many shots," he told the channel. "We were all evacuated to the roof. After several minutes, the men fled, after having continued firing in the middle of the street."

Witnesses also spoke of seeing a rocket launcher, according to French media reports.

There has been no claim of responsibility.

Satirical magazine has drawn anger

The satirical magazine is no stranger to controversy for having lampooned a variety of subjects, including Christianity. But what it's done on Islam has gotten the most attention and garnered the most vitriol.

Its last tweet before Wednesday's attack featured a cartoon of ISIS leader Abu Bakr al-Baghdadi and the words, "And, above all, health."