Hall said it was in a derelict building not in use for anything.
"We managed to get the fire under control quite quickly but unfortunately there were some casualties, with two people taken to hospital with burns and a further [three] with smoke inhalation."
Anyone who saw any unusual activity near the property on Heretaunga St West is being urged to called Hastings Police on (06) 873 0500 or Crimestoppers anonymously on 0800 555 111.