A Work and Income building was ram-raided and then set alight in the early hours of Christmas Day.

Police said a van was driven through the front of the Work and Income building in Alfred Street, Blenheim about 5am.

An accelerant was then poured around the building and set on fire, police said.

A sprinkler system and alarms in the building were activated and dampened down the blaze.

A 60-year-old Blenheim man was arrested at the scene. He was treated for smoke inhalation and was now being interviewed by police.