An investigation involving the Fire Service and the police is underway after an early morning attack on the Work and Income office in Blenheim.
Police said a van was driven through the front doors of the Alfred Street offices just after 5am and it appeared an accelerant was poured around the building and set alight.
A 60-year-old man, who was found inside the building, was arrested and had been charged with arson and burglary.
He was interviewed after being treated for smoke inhalation.
No one else was inside the building at the time.
Blenheim police sergeant Jason Munro said the motive for the attack was still unclear.
The Fire Service said there was a small fire, but sprinklers saved the building although some of the offices have suffered smoke and water damage.
The arrested man was in custody and would appear in the Blenheim District Court tomorrow.