A fire in an apartment building in northern Paris early Wednesday that killed eight people, including two children, might have been started intentionally, officials said.

The blaze in the 18th district of the French capital took more than 100 firefighters to contain it.

Criminal investigators have taken over the probe after it emerged the fire -- the deadliest in Paris since 2005 -- broke out in two separate places in the building.

A spokesman for the interior ministry, Pierre-Henry Brandet, said: "It's clear that when you have two (firefighter) call-outs in the same night ... this could be a malicious act."

Firefighters were first called to the scene at 2:20 am (0020 GMT) and quickly put out the blaze, but they were then called back again two hours later to extinguish a second, much larger fire.

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.

Interior Minister Bernard Cazeneuve, who went to the scene, said in addition to the eight dead, four were in a critical condition.

He said it was "too early to determine the causes of this tragedy".

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

The fire started on the ground floor of the building before spreading into the stairwell.

Paris mayor Anne Hidalgo said around 15 buildings in the working-class area of the district had been affected by the inferno.

The main apartment block affected was a private building, not a block of flats for low-income families, she added.