French massacre suspects 'cornered'

Two brothers suspected of slaughtering 12 people in an attack on French magazine Charlie Hebdo are holding one person hostage as police corner the gunmen northeast of the capital.

The hostage drama unfolded at a printing business in the small town of Dammartin-en-Goele, only 12 kilometres from Paris' main Charles de Gaulle airport, police sources said.

Interior Minister Bernard Cazeneuve confirmed that an operation was under way to "neutralise" the suspects as the massive manhunt appeared to be reaching a climax with helicopters buzzing overhead and a huge deployment of security forces.

"An operation is under way which is set to neutralise the perpetrators of the cowardly attack carried out two days ago," Cazeneuve said in a televised statement.

There is "near certainty" that the brothers are in the surrounded industrial building, Interior Ministry spokesman Pierre-Henry Brandet told broadcaster BFMTV.

Police had already exchanged fire with the pair in a high-speed car chase.

Prosecutors said there had been "no casualties reported" in the immediate aftermath of the shoot-out.

Prior to the standoff, the suspects had hijacked a Peugeot 206 nearby from a woman who said she recognised them as the brothers, Cherif and Said Kouachi, accused of killing 12 people in Wednesday's attack on the satirical weekly, which repeatedly lampooned the Prophet Mohammed.

President Francois Hollande rushed to the interior meeting to be briefed on the situation as Prime Minister Manuel Valls declared that France was at "war" with terrorism, but "not in a war against religion."

"It will without doubt be necessary to take measures" to respond to the terrorist "threat," he said.

Two Air France planes were forced to abort their landing at Paris's main Charles-de-Gaulle airport and go round again "due to the presence of helicopters... flying over the zone at low-altitude," the airline said.

Wednesday's bloodbath at Charlie Hebdo in Paris has sparked a global chorus of outrage, with impromptu and poignant rallies around the world in support of press freedom under the banner "jesuischarlie" (I am Charlie).

As a politically divided and crisis-hit France sought to pull together after the tragedy, the head of the country's Muslim community - the largest in Europe - urged imams to condemn terrorism at Friday prayers.

In a highly unusual step, President Francois Hollande was due to meet Front National leader Marine Le Pen at the Elysee Palace on Friday, as France geared up for a "Republican march" on Sunday expected to draw hundreds of thousands.

Refusing to be cowed, the controversial magazine plans a print run of one million copies instead of its usual 60,000, as journalists from all over the French media landscape piled in to help out the decimated staff.

"It's very hard. We are all suffering, with grief, with fear, but we will do it anyway because stupidity will not win," said columnist Patrick Pelloux.