Fireworks have been put through the letterboxes of six county properties in the last three weeks.
There have been two incidents in Northampton, one in Towcester, two in Wellingborough and one in Corby.
While any fire can have life-threatening consequences, the most serious fires to date have taken place this week, when fireworks were put through letterboxes in Caernarvon Close, Towcester, Compton Road, Wellingborough and Wareham Green, Corby, causing fire damage to the properties and putting lives at risk.
In recent weeks there have been a number of similar incidents in other parts of the UK, resulting in rescues from house fires caused by what is deemed to be a prank by some members of the community.
Mick Rodden from the Northamptonshire Arson Task Force (Fire), said: “We are shocked and dismayed by these thoughtless acts.
“What is thought to be a bit of fun can lead to the deaths of whole families.
“When any fire is started it has the potential for rapid uncontrolled spread which can engulf a house and entrap the occupants in a few minutes.”
Shaun Johnson Arson Task Force (Police) added: “These are reckless acts which can carry a life sentence on conviction.”
Investigations are continuing.
Anyone with information about any of these incidents can call Northamptonshire Police on 101 or Crimestoppers 0800 555111.