A minute’s silence is to be observed in schools across France at 10am tomorrow (9am Irish time) morning to remember the three children and a teacher killed in today's gun attack at a Jewish school in Toulouse.

French President Nicolas Sarkozy has put the southwestern region on its highest terror alert level.

Police said the gun used is the same one that was involved in two other shootings in which three soldiers were killed in the Toulouse area earlier this month.

President Sarkozy condemned the attack on the school and declared it a "national tragedy".

Mourners gathered for an overnight vigil at the Ozar Hatorah school in a leafy residential neighbourhood in Toulouse, where the gunman killed a 30-year old rabbi Jonathan Sandler, his children aged four and five, and another child, the daughter of the school's principal.

The seven-year-old girl, Miriam Monsonego, died in her father's arms as medics tried to resuscitate her.

Military police reinforcements were rushed into the area and guards were deployed at mosques and synagogues in the region.

In the United States, New York police ramped up security at synagogues and other Jewish institutions citywide.

Video surveillance footage showed the gunman bursting into the school and shooting one child at close range in the head, before fleeing on a motorbike, said Nicolas Yardeni, regional head of the French Jewish umbrella association, CRIF.

It was the worst anti-Semitic incident in France since August 1982, when six people were killed in a grenade attack and subsequent shooting at the Goldenberg restaurant in a Jewish neighbourhood of central Paris.

France's 600,000-strong Jewish community is Europe's largest.

Mr Sarkozy and Francois Hollande, the Socialist opposing him in his uphill bid for re-election in May, both rushed to the scene.

"Barbarity, savagery and cruelty cannot win, hate cannot win. The republic is much stronger than all this," Mr Sarkozy said, announcing a minute of silence in schools tomorrow.

"One can imagine that the bloodthirsty madness was linked to racism," Mr Sarkozy said, declaring he would suspend his campaign until Wednesday, when he would attend the soldiers' funeral.

Some 120 investigators were working on a manhunt for the killer and had already identified the licence plate of the motor bike used in the attack, police sources said. The gunman used a second gun when the first jammed, the Toulouse prosecutor said.

Police cordoned off the school, where well-wishers had begun to lay wreaths of flowers outside the bullet-marked walls as a line of police stood guard.