"It is horror," Hollande said in a brief statement on television, adding that a cabinet meeting had been called.
"A state of emergency will be declared," he said. "The second measure will be the closure of national borders," he added.
"We must ensure that no one comes in to commit any act whatsoever, and at the same time make sure that those who have committed these crimes should be arrested if they try to leave the country, he added.
Hollande said he had asked for military reinforcements in the Paris area to ensure that no attack can again take place.