Huge security deployment for Paris march

France's security forces plan to deploy massively for a march in honour of victims of the Paris attacks, with up to a million people expected, including several heads of state.

European leaders including German Chancellor Angela Merkel and British Prime Minister David Cameron were to attend Sunday's rally in solidarity with France, badly shaken by the attacks that left 17 people dead.

Thousands of members of the security forces are expected to be mobilised, including soldiers, along with aerial surveillance.

"What is usually done for a large rally will be doubled, even tripled, given the threat and the personalities present," a police source said without providing further details, with deployment plans expected to be finalised on Saturday night.

Prime Minister Manuel Valls and Interior Minister Bernard Cazeneuve had both spoken earlier of a massive security deployment.

Cazeneuve also said the highest possible security level in the Paris area was being maintained for now, with President Francois Hollande having warned that the threats facing France were not over.

A police source said authorities would have to be particularly alert to the possibility of someone seeking to drive into the march, embedding themselves within it or taking up a position on nearby rooftops or balconies.

Police in plainclothes will be stationed within and around the march to detect any potential threats.

The march is to take place in eastern Paris between Place de la Nation and Place de la Republique, near the offices of satirical newspaper Charlie Hebdo, where two Islamist gunmen killed 12 people on Wednesday.

The same route is used often for marches in Paris, which are organised by labour unions fairly regularly, and as a result is familiar to the security forces.

"It can accommodate several hundred thousand people without posing major logistical difficulties," the police source said.

Public transport will be free to ease access into and throughout Paris.