French police officers will be allowed to carry their weapon while off duty to protect civilians as long as France maintains the state of emergency following the Paris shootings, police said on Thursday.

French police spokesman Jerome Bonnet told BFM TV that police officers who volunteer would be able to carry their handgun in order to "protect themselves and the population in public places".

Police authorities have sent a note allowing this to all units, France Inter radio said on Thursday.

"This will allow off-duty police offers to be an additional force outside their hours," police union official Jean-Marc Bailleul said on ITELE television.

He added that off-duty policemen carrying their gun would have to wear an arm band to identify them as such.

Prime Minister Manuel Valls warned on Thursday of the danger of an attack in France using "chemical or biological weapons", in a speech to lawmakers debating the extension of a state of emergency.

"We must not rule anything out," Valls said. "There is also the risk from chemical or biological weapons," he added, as parliament debated measures to be taken in the wake of the DAESH attacks in Paris.

France has been in a state of emergency since gunmen and suicide bombers killed 129 people in a series of attacks, claimed by DAESH, in Paris last Friday.