A New Jersey family’s dream home has descended into a nightmare after a stalker, who calls themselves "The Watcher", began sending terrorising letters to their house.

The family are suing the previous owners, claiming that they knew of the The Watcher’s letters but failed to disclose any information while selling the property.

The letters began arriving on June 5 2014, three days after the family purchased the six- bedroomed property in Westfield, Union County for $1.3 million. They have caused the family so much distress that they have not yet moved into the multi-million dollar home they purchased over a year ago.

A Union County lawsuit contends that the original owners deliberately withheld information about the anonymous, sinister notes.

According to Courthouse News Service, the suit, filed earlier this month, says, “Currently, plaintiffs are in the process of selling the home as they are unable to live in the home without extreme anxiety and fear for their children's safety and well-being.”

"Plaintiffs are having trouble selling the home as interested parties, once notified of the letters, no longer view the property as a safe home."

The mysterious letters, which the suit claims show The Watcher’s "mentally disturbed fixation and claim to possession and/or ownership of the home", declare that the house has been in The Watcher’s family for decades.

“Why are you here? I will find out,” read one of the letters. "My grandfather watched the house in the 1920s and my father watched in the 1960s. It is now my time."

The letters became increasingly disturbing with further notes reading: "Have they found what is in the walls yet? In time they will. I am pleased to know your names and the names now of the young blood you have brought to me."

"Will the young bloods play in the basement. Who has the rooms facing the street? I'll know as soon as you move in. It will help me to know who is in which bedroom then I can plan better."

The new owners claim that the sellers received a letter from "The Watcher" just a week before closing on the sale. The suit says that the sellers were "so desperate to sell the million-dollar home [they] knowingly and willfully failed to disclose … this disturbing letter."

Charles Sullivan, a law professor at Seton Hall Law School, told nj.com that some US states have laws which stipulate that any tragic incidents that have a occured in a property such as murders must be disclosed when selling. "There's a duty on the part of the seller to disclose to the buyer any defect that would impact the marketability of a property," said Mr Sullivan.

New Jersey, however, does not have such laws. Mr Sullivan said: "There probably would not be a duty to disclose this."