Stock at a Northumberland charity shop was damaged by smoke when an industrial wheelie bin outside was set alight.
The incident at the back of the British Heart Foundation shop on Bridge Street in Morpeth on Saturday morning is being treated as arson.
It is also being linked to a similar fire outside the Oxfam shop on the same street less than an hour earlier.
Officers want to trace a man in a grey hooded top seen near the Oxfam shop bin shortly before the fire was discovered.
A Northumbria Police spokesman said: "It is particularly disappointing that someone would apparently choose to cause damage to a charity shop which aims to raise funds to help people, and we want to find the person or people responsible for these incidents."
Anyone with information about the incidents at 0550 and O630 GMT is asked to contact police.