Police have put security in place for two Christchurch families who have received letters demanding money and threatening to harm their children if the payment isn't made.
The two families targetted by the threats have children who go to Mount Pleasant School.
A team of detectives is working to find out who's behind the extortion attempt against the families in the past week.
The school has issued a brief statement this evening saying that of the two letters received by families, one referred directly to the students of Mount Pleasant School.
Principal Chris Nord said the school had put additional measures in place to ensure the safety of their students.
Detective Inspector Greg Murton said while there was no evidence of a genuine threat, the police were taking the matter seriously and working to identify who was behind them.
Parents had been advised of the letters and police want anyone who received any similar correspondence to contact them immediately.
The police would not confirm how the letters were delivered.