Sergeant Graham Single said that in both instances the fires were extinguished before further damage could be done.
"This sort of behaviour has the potential to cause significant damage to property and risk to others and we are very keen to identify those involved before someone's life is put at risk."
Police would like to hear from anyone who saw any activity that may be related to these incidents or from anyone who had information that may help identify the offenders, he said.
Anyone who may have been the victim of a similar offending was also asked to contact Blenheim Police on 03 578 5279 or anonymously contact Crimestoppers on 0800 555 111.