A further two youths, both aged 16, have been arrested and charged with two arson attacks in Carterton on Sunday.
The arson charges come after the arrest of a 15-year-old male on Thursday, who has also been charged with deliberately setting fire to the same two buildings.
A new unoccupied two-unit block in Belvedere Rd, Carterton, was badly damaged around 9.30pm on Sunday. The Carterton Baptist Church was broken into and a small fire started in the kitchen around 11.20pm the same night.
The charges involving the three youths were not related to the Cockburn St, Masterton, arson also on Sunday, Masterton police Senior Sergeant Carolyn Watson said.
The two 16-year-olds will appear in Masterton Youth Court next week.
The New Zealand Fire Service's senior fire risk management officer for the lower North Island, Peter Fox, said it was unusual for young people to be responsible for arson.
Mr Fox said that in the past some schools had been targeted by arsonists and young people were sometimes responsible for rubbish bin fires or small fires.
But it was unusual for young people to be involved in the sort of fire that did such damage in the two Carterton arsons.
Mr Fox said winter was a time when more fires happened.
"It's all sorts - chimney fires, clothing too close to heaters, electric blankets being folded and catching on fire, a range of different types of fires."
He said the best prevention was simply fire awareness.
"It's being aware, more than anything else. For example, electric blankets rolling them up rather than folding them up, candles, keeping matches and lighters away from children."
Mr Fox said there was little people could do to prevent the risk of arson but working smoke alarms were important.
"Be aware of the damage fire can cause, even a small fire can turn into a major fire."