Sooke's fire chief is sounding the alarm over a possible serial arsonist on Vancouver Island, after five suspicious fires in four months.

Chief Steven Sorenson says the fifth and latest blaze under criminal investigation is a fire that destroyed a mobile home in Sooke last weekend.

Sorenson says most of the five fires were started on the outside of abandoned buildings, although there had been exceptions.

"We have had a few where lives are possibly at risk and that of course, worries us more than anything," said Sorenson.

"Most of them seem to have been set with stuff that was readily available, so like leaving cardboard and paper products out seems to be an invitation sometimes."

Sorenson is warning Sooke residents not to leave recycling or other easily combustible products outside.