The masked gunmen who attacked the Paris offices of a weekly satirical magazine on Wednesday morning forced their way into Charlie Hebdo's office complex after threatening a female cartoonist.

Corrine Rey, a young mother and cartoonist, had returned from picking up her young daughter from daycare when she was confronted at the building's entrance by two heavily armed men wearing ski masks, suspected to be members of Al-Qaeda, The Telegraph reported.

"I had gone to pick up my daughter at day care, arriving in front of the magazine building, where two masked and armed men brutally threatened us," said Rey, who draws under the name "Coco."

"They said they wanted to go up to the offices, so I tapped in the code," she said, referring to the digital-code security system on the inter-phone.

After entering the access code into the security system, she and her daughter hid under a desk and watched as two other cartoonists were executed.

"They shot Wolinski and Cabu. It lasted five minutes. I had taken refuge under a desk." 

Four cartoonists were eventually killed by the masked gunmen, including Cabu, Wolinski, Tignous and Charb, the pen name of Stephane Charbonnier, also the chief editor at Charlie Hebdo, according to Charlie Hebdo's lawyer.

The killers "spoke French perfectly" and claimed to be "Al Qaeda terrorists," she told French publication L'Humanite.

Florence Pouvil, a sales assistant who worked at Lunas France, opposite the Charlie Hebdo offices, also witnessed the moment the gunmen broke in, UK MailOnline reported.

"I saw two people with big guns, like Kalashnekovs outside our office and then we heard firing. We were very confused," she said. "There were two guys who came out of the building and shot everywhere. We hid on the floor, we were terrified."

"They were wearing military clothes, it wasn't common clothing, like they were soldiers."

Although the building had security, it proved to be "useless," according to a witness who arrived just after the attack.

"There was protection at the door but they killed the police officers," Stefan De Vries told Sky News. "They executed them and they started shooting in the offices. There were more than 50 people inside."

After the gunmen escaped in a hijacked car, police officers engaged in a gunfight with them until the suspects fled away towards east Paris, along with a third armed man, according to Biz Pac Review.

Meanwhile, since the French newspaper was known to have a history of drawing outrage across the Muslim world because of its crude Islamic cartoons, it had often been a prime terrorist target for its provocative publications on Islam's holiest figure, Prophet Muhammad.

In November 2011, Charlie Hebdo was attacked after the magazine published a spoof issue that "invited" Prophet Muhammad to be its guest editor and put his caricature on the cover. On the following day, the offices of the magazine were firebombed and its website hacked, but there were no injuries.