The five bodies were found in a flat in Meaux, on the outskirts of Paris late on Christmas Day after what authorities called an "exceptionally violent crime".

The children's father was arrested Tuesday and is the primary suspect.

Meaux prosecutor Jean-Baptiste Bladier said the mother and two daughters, ages seven and 10, were stabbed several times overnight from Sunday to Monday.

The couple's two sons, ages nine months and four years old, were suffocated or drowned, he added.

The prosecutor described a small, blood-stained apartment in "extreme disarray".

The suspect, a 33-year-old man, was arrested Tuesday outside his father's home northeast of the French capital, the prosecutor said.

The suspect had stabbed his partner once before, the prosecutor said, when she was pregnant with their older son in 2019.

That investigation was dropped because he was declared mentally unsound at the time of the attack, he added.

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The suspect had been placed in a psychiatric hospital in 2017, and also attempted suicide that year, the prosecutor said.

Authorities say they are opening an investigation into five homicides, and the suspect will undergo psychiatric examination to determine the next steps.

Meaux mayor Jean-Francois Cope said: "The human toll is horrifying. A whole family was killed, stabbed in atrocious conditions. It's an absolute horror.

Mayor Cope also called for coordinated action to address violence by people with psychiatric problems and to protect victims before it's too late.

"I recognise the feeling of helplessness in such an event, but on a national level we need to have a deep assessment and rethinking of the consequences of psychiatric troubles on the families of these individuals," he said.

A neighbour of the family said the local community had "a big knot in our stomachs when [they] learned what happened".

"We cannot even imagine the scene," they added.