French police have arrested a man after eight people, including two children, were killed in a fire in a Paris apartment building that investigators believe may have been started deliberately.

More than 100 firefighters battled the blaze in the 18th district of the French capital, at the foot of the Montmartre hill and its tourist attractions.

The fire — the deadliest in Paris since 2005 — quickly became a criminal investigation after it emerged it had broken out in two separate places in the building.

Police arrested a man in his 30s "who might have been at the scene" of the fire, a source at the Paris prosecutor's office said, although he stressed the investigation was at an early stage.

The arrest was made on the basis of eyewitness accounts and CCTV footage, the source added.

Tissem Ferjani, a pastry chef who lives on the same road, said she had seen "lifeless bodies on the ground" after residents had jumped in a desperate effort to escape the raging flames.

"I was woken up around 4:00am by people screaming for help. They had no choice — either they stayed where they were and died or they got out through the window and they fell," she said.

"Everyone in the district came out to try to help them."

Interior minister Bernard Cazeneuve told Europe 1 radio that authorities were "focusing on the possibility of criminal intent".

"Nothing has been proven yet so we have to be cautious, but for the moment that is the line of investigation that is being looked at very closely," he said.

The fire is thought to be one of the worst in Paris for several years.

Firefighters were first called to the scene at 2:20am local time and quickly put out the blaze, but they were called back again two hours later to extinguish a second, much larger fire.

The blaze started on the ground floor of the five-storey building before spreading into the stairwell.

The eight victims included two who died after they attempted to escape through windows, according to police. A source close to the investigation said two children were among the victims.

Paris mayor Anne Hidalgo said the apartment block was a privately-owned building, not a block of flats for low-income families.

It had been recently renovated and was equipped with an entry code system.

The mayor said 15 buildings in the district had been affected by the inferno.

In a statement, president Francois Hollande said: "Everything is being done to shed light on the cause of this tragedy."

AFP