The rains set off dangerous mudslides, inundated homes and destroyed bridges
A six-month-old baby was among the dead, and a three-year-old child was seriously wounded by the suspect before he was shot and injured by police.
One of two police officers who were fired upon by the attacker died of his injuries.
The circumstances and motive for the killings near the town of Roye have yet to be established, police sources said.
The suspect is a member of the same travelling community, local deputy mayor Freddy Cantrel told BFM TV.