French firefighters found five people dead, including a toddler, on Tuesday (Jul 10) after a suspected domestic dispute in an apartment in the southwestern town of Pau, reports Channel NewsAsia.
The fire service was called to the apartment in the centre of Pau at 6.40am local time after neighbours saw smoke coming from it.
A neighbour "was concerned after seeing blood running down the edge of one of the apartment's windows" and tried unsuccessfully to open the door of the first-floor apartment, the emergency services said.
"I saw blood trickling [from the window] on the street side," another neighbour, who was among around 20 residents evacuated from the four-storey building, told AFP.
The neighbour said that a French man and his Spanish wife were living in the apartment with their two-year-old child and that the woman's parents had been visiting from Spain.
"A big argument broke out at around 5.00am and I heard a child crying," she said.
Inside the firefighters found the bodies of two couples and the child, and a couch ablaze.
A source close to the inquiry told AFP the young woman was "bound and gagged with tape around her neck."
The bodies of her parents also bore signs of violence, investigators said.
The child appeared to have died from smoke inhalation.
The victims had yet to be identified.